Merge tag 'phy-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/phy/linux-phy

[linux.git] / mm / memory-failure.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2008, 2009 Intel Corporation
 * Authors: Andi Kleen, Fengguang Wu
 *
 * High level machine check handler. Handles pages reported by the
 * hardware as being corrupted usually due to a multi-bit ECC memory or cache
 * failure.
 *
 * In addition there is a "soft offline" entry point that allows stop using
 * not-yet-corrupted-by-suspicious pages without killing anything.
 *
 * Handles page cache pages in various states.  The tricky part
 * here is that we can access any page asynchronously in respect to
 * other VM users, because memory failures could happen anytime and
 * anywhere. This could violate some of their assumptions. This is why
 * this code has to be extremely careful. Generally it tries to use
 * normal locking rules, as in get the standard locks, even if that means
 * the error handling takes potentially a long time.
 *
 * It can be very tempting to add handling for obscure cases here.
 * In general any code for handling new cases should only be added iff:
 * - You know how to test it.
 * - You have a test that can be added to mce-test
 *   https://git.kernel.org/cgit/utils/cpu/mce/mce-test.git/
 * - The case actually shows up as a frequent (top 10) page state in
 *   tools/mm/page-types when running a real workload.
 *
 * There are several operations here with exponential complexity because
 * of unsuitable VM data structures. For example the operation to map back
 * from RMAP chains to processes has to walk the complete process list and
 * has non linear complexity with the number. But since memory corruptions
 * are rare we hope to get away with this. This avoids impacting the core
 * VM.
 */

#define pr_fmt(fmt) "Memory failure: " fmt

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/dax.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/export.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/backing-dev.h>
#include <linux/migrate.h>
#include <linux/slab.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memory_hotplug.h>
#include <linux/mm_inline.h>
#include <linux/memremap.h>
#include <linux/kfifo.h>
#include <linux/ratelimit.h>
#include <linux/pagewalk.h>
#include <linux/shmem_fs.h>
#include <linux/sysctl.h>
#include "swap.h"
#include "internal.h"
#include "ras/ras_event.h"

static int sysctl_memory_failure_early_kill __read_mostly;

static int sysctl_memory_failure_recovery __read_mostly = 1;

static int sysctl_enable_soft_offline __read_mostly = 1;

atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);

static bool hw_memory_failure __read_mostly = false;

static DEFINE_MUTEX(mf_mutex);

void num_poisoned_pages_inc(unsigned long pfn)
{
        atomic_long_inc(&num_poisoned_pages);
        memblk_nr_poison_inc(pfn);
}

void num_poisoned_pages_sub(unsigned long pfn, long i)
{
        atomic_long_sub(i, &num_poisoned_pages);
        if (pfn != -1UL)
                memblk_nr_poison_sub(pfn, i);
}

/**
 * MF_ATTR_RO - Create sysfs entry for each memory failure statistics.
 * @_name: name of the file in the per NUMA sysfs directory.
 */
#define MF_ATTR_RO(_name)                                       \
static ssize_t _name##_show(struct device *dev,                 \
                            struct device_attribute *attr,      \
                            char *buf)                          \
{                                                               \
        struct memory_failure_stats *mf_stats =                 \
                &NODE_DATA(dev->id)->mf_stats;                  \
        return sprintf(buf, "%lu\n", mf_stats->_name);          \
}                                                               \
static DEVICE_ATTR_RO(_name)

MF_ATTR_RO(total);
MF_ATTR_RO(ignored);
MF_ATTR_RO(failed);
MF_ATTR_RO(delayed);
MF_ATTR_RO(recovered);

static struct attribute *memory_failure_attr[] = {
        &dev_attr_total.attr,
        &dev_attr_ignored.attr,
        &dev_attr_failed.attr,
        &dev_attr_delayed.attr,
        &dev_attr_recovered.attr,
        NULL,
};

const struct attribute_group memory_failure_attr_group = {
        .name = "memory_failure",
        .attrs = memory_failure_attr,
};

static struct ctl_table memory_failure_table[] = {
        {
                .procname       = "memory_failure_early_kill",
                .data           = &sysctl_memory_failure_early_kill,
                .maxlen         = sizeof(sysctl_memory_failure_early_kill),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
        {
                .procname       = "memory_failure_recovery",
                .data           = &sysctl_memory_failure_recovery,
                .maxlen         = sizeof(sysctl_memory_failure_recovery),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        },
        {
                .procname       = "enable_soft_offline",
                .data           = &sysctl_enable_soft_offline,
                .maxlen         = sizeof(sysctl_enable_soft_offline),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE,
        }
};

/*
 * Return values:
 *   1:   the page is dissolved (if needed) and taken off from buddy,
 *   0:   the page is dissolved (if needed) and not taken off from buddy,
 *   < 0: failed to dissolve.
 */
static int __page_handle_poison(struct page *page)
{
        int ret;

        /*
         * zone_pcp_disable() can't be used here. It will
         * hold pcp_batch_high_lock and dissolve_free_hugetlb_folio() might hold
         * cpu_hotplug_lock via static_key_slow_dec() when hugetlb vmemmap
         * optimization is enabled. This will break current lock dependency
         * chain and leads to deadlock.
         * Disabling pcp before dissolving the page was a deterministic
         * approach because we made sure that those pages cannot end up in any
         * PCP list. Draining PCP lists expels those pages to the buddy system,
         * but nothing guarantees that those pages do not get back to a PCP
         * queue if we need to refill those.
         */
        ret = dissolve_free_hugetlb_folio(page_folio(page));
        if (!ret) {
                drain_all_pages(page_zone(page));
                ret = take_page_off_buddy(page);
        }

        return ret;
}

static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
{
        if (hugepage_or_freepage) {
                /*
                 * Doing this check for free pages is also fine since
                 * dissolve_free_hugetlb_folio() returns 0 for non-hugetlb folios as well.
                 */
                if (__page_handle_poison(page) <= 0)
                        /*
                         * We could fail to take off the target page from buddy
                         * for example due to racy page allocation, but that's
                         * acceptable because soft-offlined page is not broken
                         * and if someone really want to use it, they should
                         * take it.
                         */
                        return false;
        }

        SetPageHWPoison(page);
        if (release)
                put_page(page);
        page_ref_inc(page);
        num_poisoned_pages_inc(page_to_pfn(page));

        return true;
}

#if IS_ENABLED(CONFIG_HWPOISON_INJECT)

u32 hwpoison_filter_enable = 0;
u32 hwpoison_filter_dev_major = ~0U;
u32 hwpoison_filter_dev_minor = ~0U;
u64 hwpoison_filter_flags_mask;
u64 hwpoison_filter_flags_value;
EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);

static int hwpoison_filter_dev(struct page *p)
{
        struct folio *folio = page_folio(p);
        struct address_space *mapping;
        dev_t dev;

        if (hwpoison_filter_dev_major == ~0U &&
            hwpoison_filter_dev_minor == ~0U)
                return 0;

        mapping = folio_mapping(folio);
        if (mapping == NULL || mapping->host == NULL)
                return -EINVAL;

        dev = mapping->host->i_sb->s_dev;
        if (hwpoison_filter_dev_major != ~0U &&
            hwpoison_filter_dev_major != MAJOR(dev))
                return -EINVAL;
        if (hwpoison_filter_dev_minor != ~0U &&
            hwpoison_filter_dev_minor != MINOR(dev))
                return -EINVAL;

        return 0;
}

static int hwpoison_filter_flags(struct page *p)
{
        if (!hwpoison_filter_flags_mask)
                return 0;

        if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
                                    hwpoison_filter_flags_value)
                return 0;
        else
                return -EINVAL;
}

/*
 * This allows stress tests to limit test scope to a collection of tasks
 * by putting them under some memcg. This prevents killing unrelated/important
 * processes such as /sbin/init. Note that the target task may share clean
 * pages with init (eg. libc text), which is harmless. If the target task
 * share _dirty_ pages with another task B, the test scheme must make sure B
 * is also included in the memcg. At last, due to race conditions this filter
 * can only guarantee that the page either belongs to the memcg tasks, or is
 * a freed page.
 */
#ifdef CONFIG_MEMCG
u64 hwpoison_filter_memcg;
EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
static int hwpoison_filter_task(struct page *p)
{
        if (!hwpoison_filter_memcg)
                return 0;

        if (page_cgroup_ino(p) != hwpoison_filter_memcg)
                return -EINVAL;

        return 0;
}
#else
static int hwpoison_filter_task(struct page *p) { return 0; }
#endif

int hwpoison_filter(struct page *p)
{
        if (!hwpoison_filter_enable)
                return 0;

        if (hwpoison_filter_dev(p))
                return -EINVAL;

        if (hwpoison_filter_flags(p))
                return -EINVAL;

        if (hwpoison_filter_task(p))
                return -EINVAL;

        return 0;
}
EXPORT_SYMBOL_GPL(hwpoison_filter);
#else
int hwpoison_filter(struct page *p)
{
        return 0;
}
#endif

/*
 * Kill all processes that have a poisoned page mapped and then isolate
 * the page.
 *
 * General strategy:
 * Find all processes having the page mapped and kill them.
 * But we keep a page reference around so that the page is not
 * actually freed yet.
 * Then stash the page away
 *
 * There's no convenient way to get back to mapped processes
 * from the VMAs. So do a brute-force search over all
 * running processes.
 *
 * Remember that machine checks are not common (or rather
 * if they are common you have other problems), so this shouldn't
 * be a performance issue.
 *
 * Also there are some races possible while we get from the
 * error detection to actually handle it.
 */

struct to_kill {
        struct list_head nd;
        struct task_struct *tsk;
        unsigned long addr;
        short size_shift;
};

/*
 * Send all the processes who have the page mapped a signal.
 * ``action optional'' if they are not immediately affected by the error
 * ``action required'' if error happened in current execution context
 */
static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
{
        struct task_struct *t = tk->tsk;
        short addr_lsb = tk->size_shift;
        int ret = 0;

        pr_err("%#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
                        pfn, t->comm, task_pid_nr(t));

        if ((flags & MF_ACTION_REQUIRED) && (t == current))
                ret = force_sig_mceerr(BUS_MCEERR_AR,
                                 (void __user *)tk->addr, addr_lsb);
        else
                /*
                 * Signal other processes sharing the page if they have
                 * PF_MCE_EARLY set.
                 * Don't use force here, it's convenient if the signal
                 * can be temporarily blocked.
                 */
                ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
                                      addr_lsb, t);
        if (ret < 0)
                pr_info("Error sending signal to %s:%d: %d\n",
                        t->comm, task_pid_nr(t), ret);
        return ret;
}

/*
 * Unknown page type encountered. Try to check whether it can turn PageLRU by
 * lru_add_drain_all.
 */
void shake_folio(struct folio *folio)
{
        if (folio_test_hugetlb(folio))
                return;
        /*
         * TODO: Could shrink slab caches here if a lightweight range-based
         * shrinker will be available.
         */
        if (folio_test_slab(folio))
                return;

        lru_add_drain_all();
}
EXPORT_SYMBOL_GPL(shake_folio);

static void shake_page(struct page *page)
{
        shake_folio(page_folio(page));
}

static unsigned long dev_pagemap_mapping_shift(struct vm_area_struct *vma,
                unsigned long address)
{
        unsigned long ret = 0;
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;
        pte_t ptent;

        VM_BUG_ON_VMA(address == -EFAULT, vma);
        pgd = pgd_offset(vma->vm_mm, address);
        if (!pgd_present(*pgd))
                return 0;
        p4d = p4d_offset(pgd, address);
        if (!p4d_present(*p4d))
                return 0;
        pud = pud_offset(p4d, address);
        if (!pud_present(*pud))
                return 0;
        if (pud_devmap(*pud))
                return PUD_SHIFT;
        pmd = pmd_offset(pud, address);
        if (!pmd_present(*pmd))
                return 0;
        if (pmd_devmap(*pmd))
                return PMD_SHIFT;
        pte = pte_offset_map(pmd, address);
        if (!pte)
                return 0;
        ptent = ptep_get(pte);
        if (pte_present(ptent) && pte_devmap(ptent))
                ret = PAGE_SHIFT;
        pte_unmap(pte);
        return ret;
}

/*
 * Failure handling: if we can't find or can't kill a process there's
 * not much we can do.  We just print a message and ignore otherwise.
 */

/*
 * Schedule a process for later kill.
 * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
 */
static void __add_to_kill(struct task_struct *tsk, struct page *p,
                          struct vm_area_struct *vma, struct list_head *to_kill,
                          unsigned long addr)
{
        struct to_kill *tk;

        tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
        if (!tk) {
                pr_err("Out of memory while machine check handling\n");
                return;
        }

        tk->addr = addr;
        if (is_zone_device_page(p))
                tk->size_shift = dev_pagemap_mapping_shift(vma, tk->addr);
        else
                tk->size_shift = page_shift(compound_head(p));

        /*
         * Send SIGKILL if "tk->addr == -EFAULT". Also, as
         * "tk->size_shift" is always non-zero for !is_zone_device_page(),
         * so "tk->size_shift == 0" effectively checks no mapping on
         * ZONE_DEVICE. Indeed, when a devdax page is mmapped N times
         * to a process' address space, it's possible not all N VMAs
         * contain mappings for the page, but at least one VMA does.
         * Only deliver SIGBUS with payload derived from the VMA that
         * has a mapping for the page.
         */
        if (tk->addr == -EFAULT) {
                pr_info("Unable to find user space address %lx in %s\n",
                        page_to_pfn(p), tsk->comm);
        } else if (tk->size_shift == 0) {
                kfree(tk);
                return;
        }

        get_task_struct(tsk);
        tk->tsk = tsk;
        list_add_tail(&tk->nd, to_kill);
}

static void add_to_kill_anon_file(struct task_struct *tsk, struct page *p,
                struct vm_area_struct *vma, struct list_head *to_kill,
                unsigned long addr)
{
        if (addr == -EFAULT)
                return;
        __add_to_kill(tsk, p, vma, to_kill, addr);
}

#ifdef CONFIG_KSM
static bool task_in_to_kill_list(struct list_head *to_kill,
                                 struct task_struct *tsk)
{
        struct to_kill *tk, *next;

        list_for_each_entry_safe(tk, next, to_kill, nd) {
                if (tk->tsk == tsk)
                        return true;
        }

        return false;
}

void add_to_kill_ksm(struct task_struct *tsk, struct page *p,
                     struct vm_area_struct *vma, struct list_head *to_kill,
                     unsigned long addr)
{
        if (!task_in_to_kill_list(to_kill, tsk))
                __add_to_kill(tsk, p, vma, to_kill, addr);
}
#endif
/*
 * Kill the processes that have been collected earlier.
 *
 * Only do anything when FORCEKILL is set, otherwise just free the
 * list (this is used for clean pages which do not need killing)
 */
static void kill_procs(struct list_head *to_kill, int forcekill,
                unsigned long pfn, int flags)
{
        struct to_kill *tk, *next;

        list_for_each_entry_safe(tk, next, to_kill, nd) {
                if (forcekill) {
                        if (tk->addr == -EFAULT) {
                                pr_err("%#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
                                       pfn, tk->tsk->comm, task_pid_nr(tk->tsk));
                                do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
                                                 tk->tsk, PIDTYPE_PID);
                        }

                        /*
                         * In theory the process could have mapped
                         * something else on the address in-between. We could
                         * check for that, but we need to tell the
                         * process anyways.
                         */
                        else if (kill_proc(tk, pfn, flags) < 0)
                                pr_err("%#lx: Cannot send advisory machine check signal to %s:%d\n",
                                       pfn, tk->tsk->comm, task_pid_nr(tk->tsk));
                }
                list_del(&tk->nd);
                put_task_struct(tk->tsk);
                kfree(tk);
        }
}

/*
 * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
 * on behalf of the thread group. Return task_struct of the (first found)
 * dedicated thread if found, and return NULL otherwise.
 *
 * We already hold rcu lock in the caller, so we don't have to call
 * rcu_read_lock/unlock() in this function.
 */
static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
{
        struct task_struct *t;

        for_each_thread(tsk, t) {
                if (t->flags & PF_MCE_PROCESS) {
                        if (t->flags & PF_MCE_EARLY)
                                return t;
                } else {
                        if (sysctl_memory_failure_early_kill)
                                return t;
                }
        }
        return NULL;
}

/*
 * Determine whether a given process is "early kill" process which expects
 * to be signaled when some page under the process is hwpoisoned.
 * Return task_struct of the dedicated thread (main thread unless explicitly
 * specified) if the process is "early kill" and otherwise returns NULL.
 *
 * Note that the above is true for Action Optional case. For Action Required
 * case, it's only meaningful to the current thread which need to be signaled
 * with SIGBUS, this error is Action Optional for other non current
 * processes sharing the same error page,if the process is "early kill", the
 * task_struct of the dedicated thread will also be returned.
 */
struct task_struct *task_early_kill(struct task_struct *tsk, int force_early)
{
        if (!tsk->mm)
                return NULL;
        /*
         * Comparing ->mm here because current task might represent
         * a subthread, while tsk always points to the main thread.
         */
        if (force_early && tsk->mm == current->mm)
                return current;

        return find_early_kill_thread(tsk);
}

/*
 * Collect processes when the error hit an anonymous page.
 */
static void collect_procs_anon(struct folio *folio, struct page *page,
                struct list_head *to_kill, int force_early)
{
        struct task_struct *tsk;
        struct anon_vma *av;
        pgoff_t pgoff;

        av = folio_lock_anon_vma_read(folio, NULL);
        if (av == NULL) /* Not actually mapped anymore */
                return;

        pgoff = page_to_pgoff(page);
        rcu_read_lock();
        for_each_process(tsk) {
                struct vm_area_struct *vma;
                struct anon_vma_chain *vmac;
                struct task_struct *t = task_early_kill(tsk, force_early);
                unsigned long addr;

                if (!t)
                        continue;
                anon_vma_interval_tree_foreach(vmac, &av->rb_root,
                                               pgoff, pgoff) {
                        vma = vmac->vma;
                        if (vma->vm_mm != t->mm)
                                continue;
                        addr = page_mapped_in_vma(page, vma);
                        add_to_kill_anon_file(t, page, vma, to_kill, addr);
                }
        }
        rcu_read_unlock();
        anon_vma_unlock_read(av);
}

/*
 * Collect processes when the error hit a file mapped page.
 */
static void collect_procs_file(struct folio *folio, struct page *page,
                struct list_head *to_kill, int force_early)
{
        struct vm_area_struct *vma;
        struct task_struct *tsk;
        struct address_space *mapping = folio->mapping;
        pgoff_t pgoff;

        i_mmap_lock_read(mapping);
        rcu_read_lock();
        pgoff = page_to_pgoff(page);
        for_each_process(tsk) {
                struct task_struct *t = task_early_kill(tsk, force_early);
                unsigned long addr;

                if (!t)
                        continue;
                vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
                                      pgoff) {
                        /*
                         * Send early kill signal to tasks where a vma covers
                         * the page but the corrupted page is not necessarily
                         * mapped in its pte.
                         * Assume applications who requested early kill want
                         * to be informed of all such data corruptions.
                         */
                        if (vma->vm_mm != t->mm)
                                continue;
                        addr = page_address_in_vma(page, vma);
                        add_to_kill_anon_file(t, page, vma, to_kill, addr);
                }
        }
        rcu_read_unlock();
        i_mmap_unlock_read(mapping);
}

#ifdef CONFIG_FS_DAX
static void add_to_kill_fsdax(struct task_struct *tsk, struct page *p,
                              struct vm_area_struct *vma,
                              struct list_head *to_kill, pgoff_t pgoff)
{
        unsigned long addr = vma_address(vma, pgoff, 1);
        __add_to_kill(tsk, p, vma, to_kill, addr);
}

/*
 * Collect processes when the error hit a fsdax page.
 */
static void collect_procs_fsdax(struct page *page,
                struct address_space *mapping, pgoff_t pgoff,
                struct list_head *to_kill, bool pre_remove)
{
        struct vm_area_struct *vma;
        struct task_struct *tsk;

        i_mmap_lock_read(mapping);
        rcu_read_lock();
        for_each_process(tsk) {
                struct task_struct *t = tsk;

                /*
                 * Search for all tasks while MF_MEM_PRE_REMOVE is set, because
                 * the current may not be the one accessing the fsdax page.
                 * Otherwise, search for the current task.
                 */
                if (!pre_remove)
                        t = task_early_kill(tsk, true);
                if (!t)
                        continue;
                vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
                        if (vma->vm_mm == t->mm)
                                add_to_kill_fsdax(t, page, vma, to_kill, pgoff);
                }
        }
        rcu_read_unlock();
        i_mmap_unlock_read(mapping);
}
#endif /* CONFIG_FS_DAX */

/*
 * Collect the processes who have the corrupted page mapped to kill.
 */
static void collect_procs(struct folio *folio, struct page *page,
                struct list_head *tokill, int force_early)
{
        if (!folio->mapping)
                return;
        if (unlikely(folio_test_ksm(folio)))
                collect_procs_ksm(folio, page, tokill, force_early);
        else if (folio_test_anon(folio))
                collect_procs_anon(folio, page, tokill, force_early);
        else
                collect_procs_file(folio, page, tokill, force_early);
}

struct hwpoison_walk {
        struct to_kill tk;
        unsigned long pfn;
        int flags;
};

static void set_to_kill(struct to_kill *tk, unsigned long addr, short shift)
{
        tk->addr = addr;
        tk->size_shift = shift;
}

static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
                                unsigned long poisoned_pfn, struct to_kill *tk)
{
        unsigned long pfn = 0;

        if (pte_present(pte)) {
                pfn = pte_pfn(pte);
        } else {
                swp_entry_t swp = pte_to_swp_entry(pte);

                if (is_hwpoison_entry(swp))
                        pfn = swp_offset_pfn(swp);
        }

        if (!pfn || pfn != poisoned_pfn)
                return 0;

        set_to_kill(tk, addr, shift);
        return 1;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static int check_hwpoisoned_pmd_entry(pmd_t *pmdp, unsigned long addr,
                                      struct hwpoison_walk *hwp)
{
        pmd_t pmd = *pmdp;
        unsigned long pfn;
        unsigned long hwpoison_vaddr;

        if (!pmd_present(pmd))
                return 0;
        pfn = pmd_pfn(pmd);
        if (pfn <= hwp->pfn && hwp->pfn < pfn + HPAGE_PMD_NR) {
                hwpoison_vaddr = addr + ((hwp->pfn - pfn) << PAGE_SHIFT);
                set_to_kill(&hwp->tk, hwpoison_vaddr, PAGE_SHIFT);
                return 1;
        }
        return 0;
}
#else
static int check_hwpoisoned_pmd_entry(pmd_t *pmdp, unsigned long addr,
                                      struct hwpoison_walk *hwp)
{
        return 0;
}
#endif

static int hwpoison_pte_range(pmd_t *pmdp, unsigned long addr,
                              unsigned long end, struct mm_walk *walk)
{
        struct hwpoison_walk *hwp = walk->private;
        int ret = 0;
        pte_t *ptep, *mapped_pte;
        spinlock_t *ptl;

        ptl = pmd_trans_huge_lock(pmdp, walk->vma);
        if (ptl) {
                ret = check_hwpoisoned_pmd_entry(pmdp, addr, hwp);
                spin_unlock(ptl);
                goto out;
        }

        mapped_pte = ptep = pte_offset_map_lock(walk->vma->vm_mm, pmdp,
                                                addr, &ptl);
        if (!ptep)
                goto out;

        for (; addr != end; ptep++, addr += PAGE_SIZE) {
                ret = check_hwpoisoned_entry(ptep_get(ptep), addr, PAGE_SHIFT,
                                             hwp->pfn, &hwp->tk);
                if (ret == 1)
                        break;
        }
        pte_unmap_unlock(mapped_pte, ptl);
out:
        cond_resched();
        return ret;
}

#ifdef CONFIG_HUGETLB_PAGE
static int hwpoison_hugetlb_range(pte_t *ptep, unsigned long hmask,
                            unsigned long addr, unsigned long end,
                            struct mm_walk *walk)
{
        struct hwpoison_walk *hwp = walk->private;
        pte_t pte = huge_ptep_get(walk->mm, addr, ptep);
        struct hstate *h = hstate_vma(walk->vma);

        return check_hwpoisoned_entry(pte, addr, huge_page_shift(h),
                                      hwp->pfn, &hwp->tk);
}
#else
#define hwpoison_hugetlb_range  NULL
#endif

static const struct mm_walk_ops hwpoison_walk_ops = {
        .pmd_entry = hwpoison_pte_range,
        .hugetlb_entry = hwpoison_hugetlb_range,
        .walk_lock = PGWALK_RDLOCK,
};

/*
 * Sends SIGBUS to the current process with error info.
 *
 * This function is intended to handle "Action Required" MCEs on already
 * hardware poisoned pages. They could happen, for example, when
 * memory_failure() failed to unmap the error page at the first call, or
 * when multiple local machine checks happened on different CPUs.
 *
 * MCE handler currently has no easy access to the error virtual address,
 * so this function walks page table to find it. The returned virtual address
 * is proper in most cases, but it could be wrong when the application
 * process has multiple entries mapping the error page.
 */
static int kill_accessing_process(struct task_struct *p, unsigned long pfn,
                                  int flags)
{
        int ret;
        struct hwpoison_walk priv = {
                .pfn = pfn,
        };
        priv.tk.tsk = p;

        if (!p->mm)
                return -EFAULT;

        mmap_read_lock(p->mm);
        ret = walk_page_range(p->mm, 0, TASK_SIZE, &hwpoison_walk_ops,
                              (void *)&priv);
        if (ret == 1 && priv.tk.addr)
                kill_proc(&priv.tk, pfn, flags);
        else
                ret = 0;
        mmap_read_unlock(p->mm);
        return ret > 0 ? -EHWPOISON : -EFAULT;
}

/*
 * MF_IGNORED - The m-f() handler marks the page as PG_hwpoisoned'ed.
 * But it could not do more to isolate the page from being accessed again,
 * nor does it kill the process. This is extremely rare and one of the
 * potential causes is that the page state has been changed due to
 * underlying race condition. This is the most severe outcomes.
 *
 * MF_FAILED - The m-f() handler marks the page as PG_hwpoisoned'ed.
 * It should have killed the process, but it can't isolate the page,
 * due to conditions such as extra pin, unmap failure, etc. Accessing
 * the page again may trigger another MCE and the process will be killed
 * by the m-f() handler immediately.
 *
 * MF_DELAYED - The m-f() handler marks the page as PG_hwpoisoned'ed.
 * The page is unmapped, and is removed from the LRU or file mapping.
 * An attempt to access the page again will trigger page fault and the
 * PF handler will kill the process.
 *
 * MF_RECOVERED - The m-f() handler marks the page as PG_hwpoisoned'ed.
 * The page has been completely isolated, that is, unmapped, taken out of
 * the buddy system, or hole-punnched out of the file mapping.
 */
static const char *action_name[] = {
        [MF_IGNORED] = "Ignored",
        [MF_FAILED] = "Failed",
        [MF_DELAYED] = "Delayed",
        [MF_RECOVERED] = "Recovered",
};

static const char * const action_page_types[] = {
        [MF_MSG_KERNEL]                 = "reserved kernel page",
        [MF_MSG_KERNEL_HIGH_ORDER]      = "high-order kernel page",
        [MF_MSG_HUGE]                   = "huge page",
        [MF_MSG_FREE_HUGE]              = "free huge page",
        [MF_MSG_GET_HWPOISON]           = "get hwpoison page",
        [MF_MSG_UNMAP_FAILED]           = "unmapping failed page",
        [MF_MSG_DIRTY_SWAPCACHE]        = "dirty swapcache page",
        [MF_MSG_CLEAN_SWAPCACHE]        = "clean swapcache page",
        [MF_MSG_DIRTY_MLOCKED_LRU]      = "dirty mlocked LRU page",
        [MF_MSG_CLEAN_MLOCKED_LRU]      = "clean mlocked LRU page",
        [MF_MSG_DIRTY_UNEVICTABLE_LRU]  = "dirty unevictable LRU page",
        [MF_MSG_CLEAN_UNEVICTABLE_LRU]  = "clean unevictable LRU page",
        [MF_MSG_DIRTY_LRU]              = "dirty LRU page",
        [MF_MSG_CLEAN_LRU]              = "clean LRU page",
        [MF_MSG_TRUNCATED_LRU]          = "already truncated LRU page",
        [MF_MSG_BUDDY]                  = "free buddy page",
        [MF_MSG_DAX]                    = "dax page",
        [MF_MSG_UNSPLIT_THP]            = "unsplit thp",
        [MF_MSG_ALREADY_POISONED]       = "already poisoned",
        [MF_MSG_UNKNOWN]                = "unknown page",
};

/*
 * XXX: It is possible that a page is isolated from LRU cache,
 * and then kept in swap cache or failed to remove from page cache.
 * The page count will stop it from being freed by unpoison.
 * Stress tests should be aware of this memory leak problem.
 */
static int delete_from_lru_cache(struct folio *folio)
{
        if (folio_isolate_lru(folio)) {
                /*
                 * Clear sensible page flags, so that the buddy system won't
                 * complain when the folio is unpoison-and-freed.
                 */
                folio_clear_active(folio);
                folio_clear_unevictable(folio);

                /*
                 * Poisoned page might never drop its ref count to 0 so we have
                 * to uncharge it manually from its memcg.
                 */
                mem_cgroup_uncharge(folio);

                /*
                 * drop the refcount elevated by folio_isolate_lru()
                 */
                folio_put(folio);
                return 0;
        }
        return -EIO;
}

static int truncate_error_folio(struct folio *folio, unsigned long pfn,
                                struct address_space *mapping)
{
        int ret = MF_FAILED;

        if (mapping->a_ops->error_remove_folio) {
                int err = mapping->a_ops->error_remove_folio(mapping, folio);

                if (err != 0)
                        pr_info("%#lx: Failed to punch page: %d\n", pfn, err);
                else if (!filemap_release_folio(folio, GFP_NOIO))
                        pr_info("%#lx: failed to release buffers\n", pfn);
                else
                        ret = MF_RECOVERED;
        } else {
                /*
                 * If the file system doesn't support it just invalidate
                 * This fails on dirty or anything with private pages
                 */
                if (mapping_evict_folio(mapping, folio))
                        ret = MF_RECOVERED;
                else
                        pr_info("%#lx: Failed to invalidate\n", pfn);
        }

        return ret;
}

struct page_state {
        unsigned long mask;
        unsigned long res;
        enum mf_action_page_type type;

        /* Callback ->action() has to unlock the relevant page inside it. */
        int (*action)(struct page_state *ps, struct page *p);
};

/*
 * Return true if page is still referenced by others, otherwise return
 * false.
 *
 * The extra_pins is true when one extra refcount is expected.
 */
static bool has_extra_refcount(struct page_state *ps, struct page *p,
                               bool extra_pins)
{
        int count = page_count(p) - 1;

        if (extra_pins)
                count -= folio_nr_pages(page_folio(p));

        if (count > 0) {
                pr_err("%#lx: %s still referenced by %d users\n",
                       page_to_pfn(p), action_page_types[ps->type], count);
                return true;
        }

        return false;
}

/*
 * Error hit kernel page.
 * Do nothing, try to be lucky and not touch this instead. For a few cases we
 * could be more sophisticated.
 */
static int me_kernel(struct page_state *ps, struct page *p)
{
        unlock_page(p);
        return MF_IGNORED;
}

/*
 * Page in unknown state. Do nothing.
 * This is a catch-all in case we fail to make sense of the page state.
 */
static int me_unknown(struct page_state *ps, struct page *p)
{
        pr_err("%#lx: Unknown page state\n", page_to_pfn(p));
        unlock_page(p);
        return MF_IGNORED;
}

/*
 * Clean (or cleaned) page cache page.
 */
static int me_pagecache_clean(struct page_state *ps, struct page *p)
{
        struct folio *folio = page_folio(p);
        int ret;
        struct address_space *mapping;
        bool extra_pins;

        delete_from_lru_cache(folio);

        /*
         * For anonymous folios the only reference left
         * should be the one m_f() holds.
         */
        if (folio_test_anon(folio)) {
                ret = MF_RECOVERED;
                goto out;
        }

        /*
         * Now truncate the page in the page cache. This is really
         * more like a "temporary hole punch"
         * Don't do this for block devices when someone else
         * has a reference, because it could be file system metadata
         * and that's not safe to truncate.
         */
        mapping = folio_mapping(folio);
        if (!mapping) {
                /* Folio has been torn down in the meantime */
                ret = MF_FAILED;
                goto out;
        }

        /*
         * The shmem page is kept in page cache instead of truncating
         * so is expected to have an extra refcount after error-handling.
         */
        extra_pins = shmem_mapping(mapping);

        /*
         * Truncation is a bit tricky. Enable it per file system for now.
         *
         * Open: to take i_rwsem or not for this? Right now we don't.
         */
        ret = truncate_error_folio(folio, page_to_pfn(p), mapping);
        if (has_extra_refcount(ps, p, extra_pins))
                ret = MF_FAILED;

out:
        folio_unlock(folio);

        return ret;
}

/*
 * Dirty pagecache page
 * Issues: when the error hit a hole page the error is not properly
 * propagated.
 */
static int me_pagecache_dirty(struct page_state *ps, struct page *p)
{
        struct folio *folio = page_folio(p);
        struct address_space *mapping = folio_mapping(folio);

        /* TBD: print more information about the file. */
        if (mapping) {
                /*
                 * IO error will be reported by write(), fsync(), etc.
                 * who check the mapping.
                 * This way the application knows that something went
                 * wrong with its dirty file data.
                 */
                mapping_set_error(mapping, -EIO);
        }

        return me_pagecache_clean(ps, p);
}

/*
 * Clean and dirty swap cache.
 *
 * Dirty swap cache page is tricky to handle. The page could live both in page
 * table and swap cache(ie. page is freshly swapped in). So it could be
 * referenced concurrently by 2 types of PTEs:
 * normal PTEs and swap PTEs. We try to handle them consistently by calling
 * try_to_unmap(!TTU_HWPOISON) to convert the normal PTEs to swap PTEs,
 * and then
 *      - clear dirty bit to prevent IO
 *      - remove from LRU
 *      - but keep in the swap cache, so that when we return to it on
 *        a later page fault, we know the application is accessing
 *        corrupted data and shall be killed (we installed simple
 *        interception code in do_swap_page to catch it).
 *
 * Clean swap cache pages can be directly isolated. A later page fault will
 * bring in the known good data from disk.
 */
static int me_swapcache_dirty(struct page_state *ps, struct page *p)
{
        struct folio *folio = page_folio(p);
        int ret;
        bool extra_pins = false;

        folio_clear_dirty(folio);
        /* Trigger EIO in shmem: */
        folio_clear_uptodate(folio);

        ret = delete_from_lru_cache(folio) ? MF_FAILED : MF_DELAYED;
        folio_unlock(folio);

        if (ret == MF_DELAYED)
                extra_pins = true;

        if (has_extra_refcount(ps, p, extra_pins))
                ret = MF_FAILED;

        return ret;
}

static int me_swapcache_clean(struct page_state *ps, struct page *p)
{
        struct folio *folio = page_folio(p);
        int ret;

        delete_from_swap_cache(folio);

        ret = delete_from_lru_cache(folio) ? MF_FAILED : MF_RECOVERED;
        folio_unlock(folio);

        if (has_extra_refcount(ps, p, false))
                ret = MF_FAILED;

        return ret;
}

/*
 * Huge pages. Needs work.
 * Issues:
 * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
 *   To narrow down kill region to one page, we need to break up pmd.
 */
static int me_huge_page(struct page_state *ps, struct page *p)
{
        struct folio *folio = page_folio(p);
        int res;
        struct address_space *mapping;
        bool extra_pins = false;

        mapping = folio_mapping(folio);
        if (mapping) {
                res = truncate_error_folio(folio, page_to_pfn(p), mapping);
                /* The page is kept in page cache. */
                extra_pins = true;
                folio_unlock(folio);
        } else {
                folio_unlock(folio);
                /*
                 * migration entry prevents later access on error hugepage,
                 * so we can free and dissolve it into buddy to save healthy
                 * subpages.
                 */
                folio_put(folio);
                if (__page_handle_poison(p) > 0) {
                        page_ref_inc(p);
                        res = MF_RECOVERED;
                } else {
                        res = MF_FAILED;
                }
        }

        if (has_extra_refcount(ps, p, extra_pins))
                res = MF_FAILED;

        return res;
}

/*
 * Various page states we can handle.
 *
 * A page state is defined by its current page->flags bits.
 * The table matches them in order and calls the right handler.
 *
 * This is quite tricky because we can access page at any time
 * in its live cycle, so all accesses have to be extremely careful.
 *
 * This is not complete. More states could be added.
 * For any missing state don't attempt recovery.
 */

#define dirty           (1UL << PG_dirty)
#define sc              ((1UL << PG_swapcache) | (1UL << PG_swapbacked))
#define unevict         (1UL << PG_unevictable)
#define mlock           (1UL << PG_mlocked)
#define lru             (1UL << PG_lru)
#define head            (1UL << PG_head)
#define reserved        (1UL << PG_reserved)

static struct page_state error_states[] = {
        { reserved,     reserved,       MF_MSG_KERNEL,  me_kernel },
        /*
         * free pages are specially detected outside this table:
         * PG_buddy pages only make a small fraction of all free pages.
         */

        { head,         head,           MF_MSG_HUGE,            me_huge_page },

        { sc|dirty,     sc|dirty,       MF_MSG_DIRTY_SWAPCACHE, me_swapcache_dirty },
        { sc|dirty,     sc,             MF_MSG_CLEAN_SWAPCACHE, me_swapcache_clean },

        { mlock|dirty,  mlock|dirty,    MF_MSG_DIRTY_MLOCKED_LRU,       me_pagecache_dirty },
        { mlock|dirty,  mlock,          MF_MSG_CLEAN_MLOCKED_LRU,       me_pagecache_clean },

        { unevict|dirty, unevict|dirty, MF_MSG_DIRTY_UNEVICTABLE_LRU,   me_pagecache_dirty },
        { unevict|dirty, unevict,       MF_MSG_CLEAN_UNEVICTABLE_LRU,   me_pagecache_clean },

        { lru|dirty,    lru|dirty,      MF_MSG_DIRTY_LRU,       me_pagecache_dirty },
        { lru|dirty,    lru,            MF_MSG_CLEAN_LRU,       me_pagecache_clean },

        /*
         * Catchall entry: must be at end.
         */
        { 0,            0,              MF_MSG_UNKNOWN, me_unknown },
};

#undef dirty
#undef sc
#undef unevict
#undef mlock
#undef lru
#undef head
#undef reserved

static void update_per_node_mf_stats(unsigned long pfn,
                                     enum mf_result result)
{
        int nid = MAX_NUMNODES;
        struct memory_failure_stats *mf_stats = NULL;

        nid = pfn_to_nid(pfn);
        if (unlikely(nid < 0 || nid >= MAX_NUMNODES)) {
                WARN_ONCE(1, "Memory failure: pfn=%#lx, invalid nid=%d", pfn, nid);
                return;
        }

        mf_stats = &NODE_DATA(nid)->mf_stats;
        switch (result) {
        case MF_IGNORED:
                ++mf_stats->ignored;
                break;
        case MF_FAILED:
                ++mf_stats->failed;
                break;
        case MF_DELAYED:
                ++mf_stats->delayed;
                break;
        case MF_RECOVERED:
                ++mf_stats->recovered;
                break;
        default:
                WARN_ONCE(1, "Memory failure: mf_result=%d is not properly handled", result);
                break;
        }
        ++mf_stats->total;
}

/*
 * "Dirty/Clean" indication is not 100% accurate due to the possibility of
 * setting PG_dirty outside page lock. See also comment above set_page_dirty().
 */
static int action_result(unsigned long pfn, enum mf_action_page_type type,
                         enum mf_result result)
{
        trace_memory_failure_event(pfn, type, result);

        num_poisoned_pages_inc(pfn);

        update_per_node_mf_stats(pfn, result);

        pr_err("%#lx: recovery action for %s: %s\n",
                pfn, action_page_types[type], action_name[result]);

        return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
}

static int page_action(struct page_state *ps, struct page *p,
                        unsigned long pfn)
{
        int result;

        /* page p should be unlocked after returning from ps->action().  */
        result = ps->action(ps, p);

        /* Could do more checks here if page looks ok */
        /*
         * Could adjust zone counters here to correct for the missing page.
         */

        return action_result(pfn, ps->type, result);
}

static inline bool PageHWPoisonTakenOff(struct page *page)
{
        return PageHWPoison(page) && page_private(page) == MAGIC_HWPOISON;
}

void SetPageHWPoisonTakenOff(struct page *page)
{
        set_page_private(page, MAGIC_HWPOISON);
}

void ClearPageHWPoisonTakenOff(struct page *page)
{
        if (PageHWPoison(page))
                set_page_private(page, 0);
}

/*
 * Return true if a page type of a given page is supported by hwpoison
 * mechanism (while handling could fail), otherwise false.  This function
 * does not return true for hugetlb or device memory pages, so it's assumed
 * to be called only in the context where we never have such pages.
 */
static inline bool HWPoisonHandlable(struct page *page, unsigned long flags)
{
        if (PageSlab(page))
                return false;

        /* Soft offline could migrate non-LRU movable pages */
        if ((flags & MF_SOFT_OFFLINE) && __PageMovable(page))
                return true;

        return PageLRU(page) || is_free_buddy_page(page);
}

static int __get_hwpoison_page(struct page *page, unsigned long flags)
{
        struct folio *folio = page_folio(page);
        int ret = 0;
        bool hugetlb = false;

        ret = get_hwpoison_hugetlb_folio(folio, &hugetlb, false);
        if (hugetlb) {
                /* Make sure hugetlb demotion did not happen from under us. */
                if (folio == page_folio(page))
                        return ret;
                if (ret > 0) {
                        folio_put(folio);
                        folio = page_folio(page);
                }
        }

        /*
         * This check prevents from calling folio_try_get() for any
         * unsupported type of folio in order to reduce the risk of unexpected
         * races caused by taking a folio refcount.
         */
        if (!HWPoisonHandlable(&folio->page, flags))
                return -EBUSY;

        if (folio_try_get(folio)) {
                if (folio == page_folio(page))
                        return 1;

                pr_info("%#lx cannot catch tail\n", page_to_pfn(page));
                folio_put(folio);
        }

        return 0;
}

#define GET_PAGE_MAX_RETRY_NUM 3

static int get_any_page(struct page *p, unsigned long flags)
{
        int ret = 0, pass = 0;
        bool count_increased = false;

        if (flags & MF_COUNT_INCREASED)
                count_increased = true;

try_again:
        if (!count_increased) {
                ret = __get_hwpoison_page(p, flags);
                if (!ret) {
                        if (page_count(p)) {
                                /* We raced with an allocation, retry. */
                                if (pass++ < GET_PAGE_MAX_RETRY_NUM)
                                        goto try_again;
                                ret = -EBUSY;
                        } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
                                /* We raced with put_page, retry. */
                                if (pass++ < GET_PAGE_MAX_RETRY_NUM)
                                        goto try_again;
                                ret = -EIO;
                        }
                        goto out;
                } else if (ret == -EBUSY) {
                        /*
                         * We raced with (possibly temporary) unhandlable
                         * page, retry.
                         */
                        if (pass++ < 3) {
                                shake_page(p);
                                goto try_again;
                        }
                        ret = -EIO;
                        goto out;
                }
        }

        if (PageHuge(p) || HWPoisonHandlable(p, flags)) {
                ret = 1;
        } else {
                /*
                 * A page we cannot handle. Check whether we can turn
                 * it into something we can handle.
                 */
                if (pass++ < GET_PAGE_MAX_RETRY_NUM) {
                        put_page(p);
                        shake_page(p);
                        count_increased = false;
                        goto try_again;
                }
                put_page(p);
                ret = -EIO;
        }
out:
        if (ret == -EIO)
                pr_err("%#lx: unhandlable page.\n", page_to_pfn(p));

        return ret;
}

static int __get_unpoison_page(struct page *page)
{
        struct folio *folio = page_folio(page);
        int ret = 0;
        bool hugetlb = false;

        ret = get_hwpoison_hugetlb_folio(folio, &hugetlb, true);
        if (hugetlb) {
                /* Make sure hugetlb demotion did not happen from under us. */
                if (folio == page_folio(page))
                        return ret;
                if (ret > 0)
                        folio_put(folio);
        }

        /*
         * PageHWPoisonTakenOff pages are not only marked as PG_hwpoison,
         * but also isolated from buddy freelist, so need to identify the
         * state and have to cancel both operations to unpoison.
         */
        if (PageHWPoisonTakenOff(page))
                return -EHWPOISON;

        return get_page_unless_zero(page) ? 1 : 0;
}

/**
 * get_hwpoison_page() - Get refcount for memory error handling
 * @p:          Raw error page (hit by memory error)
 * @flags:      Flags controlling behavior of error handling
 *
 * get_hwpoison_page() takes a page refcount of an error page to handle memory
 * error on it, after checking that the error page is in a well-defined state
 * (defined as a page-type we can successfully handle the memory error on it,
 * such as LRU page and hugetlb page).
 *
 * Memory error handling could be triggered at any time on any type of page,
 * so it's prone to race with typical memory management lifecycle (like
 * allocation and free).  So to avoid such races, get_hwpoison_page() takes
 * extra care for the error page's state (as done in __get_hwpoison_page()),
 * and has some retry logic in get_any_page().
 *
 * When called from unpoison_memory(), the caller should already ensure that
 * the given page has PG_hwpoison. So it's never reused for other page
 * allocations, and __get_unpoison_page() never races with them.
 *
 * Return: 0 on failure or free buddy (hugetlb) page,
 *         1 on success for in-use pages in a well-defined state,
 *         -EIO for pages on which we can not handle memory errors,
 *         -EBUSY when get_hwpoison_page() has raced with page lifecycle
 *         operations like allocation and free,
 *         -EHWPOISON when the page is hwpoisoned and taken off from buddy.
 */
static int get_hwpoison_page(struct page *p, unsigned long flags)
{
        int ret;

        zone_pcp_disable(page_zone(p));
        if (flags & MF_UNPOISON)
                ret = __get_unpoison_page(p);
        else
                ret = get_any_page(p, flags);
        zone_pcp_enable(page_zone(p));

        return ret;
}

void unmap_poisoned_folio(struct folio *folio, enum ttu_flags ttu)
{
        if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
                struct address_space *mapping;

                /*
                 * For hugetlb folios in shared mappings, try_to_unmap
                 * could potentially call huge_pmd_unshare.  Because of
                 * this, take semaphore in write mode here and set
                 * TTU_RMAP_LOCKED to indicate we have taken the lock
                 * at this higher level.
                 */
                mapping = hugetlb_folio_mapping_lock_write(folio);
                if (!mapping) {
                        pr_info("%#lx: could not lock mapping for mapped hugetlb folio\n",
                                folio_pfn(folio));
                        return;
                }

                try_to_unmap(folio, ttu|TTU_RMAP_LOCKED);
                i_mmap_unlock_write(mapping);
        } else {
                try_to_unmap(folio, ttu);
        }
}

/*
 * Do all that is necessary to remove user space mappings. Unmap
 * the pages and send SIGBUS to the processes if the data was dirty.
 */
static bool hwpoison_user_mappings(struct folio *folio, struct page *p,
                unsigned long pfn, int flags)
{
        enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_SYNC | TTU_HWPOISON;
        struct address_space *mapping;
        LIST_HEAD(tokill);
        bool unmap_success;
        int forcekill;
        bool mlocked = folio_test_mlocked(folio);

        /*
         * Here we are interested only in user-mapped pages, so skip any
         * other types of pages.
         */
        if (folio_test_reserved(folio) || folio_test_slab(folio) ||
            folio_test_pgtable(folio) || folio_test_offline(folio))
                return true;
        if (!(folio_test_lru(folio) || folio_test_hugetlb(folio)))
                return true;

        /*
         * This check implies we don't kill processes if their pages
         * are in the swap cache early. Those are always late kills.
         */
        if (!folio_mapped(folio))
                return true;

        if (folio_test_swapcache(folio)) {
                pr_err("%#lx: keeping poisoned page in swap cache\n", pfn);
                ttu &= ~TTU_HWPOISON;
        }

        /*
         * Propagate the dirty bit from PTEs to struct page first, because we
         * need this to decide if we should kill or just drop the page.
         * XXX: the dirty test could be racy: set_page_dirty() may not always
         * be called inside page lock (it's recommended but not enforced).
         */
        mapping = folio_mapping(folio);
        if (!(flags & MF_MUST_KILL) && !folio_test_dirty(folio) && mapping &&
            mapping_can_writeback(mapping)) {
                if (folio_mkclean(folio)) {
                        folio_set_dirty(folio);
                } else {
                        ttu &= ~TTU_HWPOISON;
                        pr_info("%#lx: corrupted page was clean: dropped without side effects\n",
                                pfn);
                }
        }

        /*
         * First collect all the processes that have the page
         * mapped in dirty form.  This has to be done before try_to_unmap,
         * because ttu takes the rmap data structures down.
         */
        collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);

        unmap_poisoned_folio(folio, ttu);

        unmap_success = !folio_mapped(folio);
        if (!unmap_success)
                pr_err("%#lx: failed to unmap page (folio mapcount=%d)\n",
                       pfn, folio_mapcount(folio));

        /*
         * try_to_unmap() might put mlocked page in lru cache, so call
         * shake_page() again to ensure that it's flushed.
         */
        if (mlocked)
                shake_folio(folio);

        /*
         * Now that the dirty bit has been propagated to the
         * struct page and all unmaps done we can decide if
         * killing is needed or not.  Only kill when the page
         * was dirty or the process is not restartable,
         * otherwise the tokill list is merely
         * freed.  When there was a problem unmapping earlier
         * use a more force-full uncatchable kill to prevent
         * any accesses to the poisoned memory.
         */
        forcekill = folio_test_dirty(folio) || (flags & MF_MUST_KILL) ||
                    !unmap_success;
        kill_procs(&tokill, forcekill, pfn, flags);

        return unmap_success;
}

static int identify_page_state(unsigned long pfn, struct page *p,
                                unsigned long page_flags)
{
        struct page_state *ps;

        /*
         * The first check uses the current page flags which may not have any
         * relevant information. The second check with the saved page flags is
         * carried out only if the first check can't determine the page status.
         */
        for (ps = error_states;; ps++)
                if ((p->flags & ps->mask) == ps->res)
                        break;

        page_flags |= (p->flags & (1UL << PG_dirty));

        if (!ps->mask)
                for (ps = error_states;; ps++)
                        if ((page_flags & ps->mask) == ps->res)
                                break;
        return page_action(ps, p, pfn);
}

/*
 * When 'release' is 'false', it means that if thp split has failed,
 * there is still more to do, hence the page refcount we took earlier
 * is still needed.
 */
static int try_to_split_thp_page(struct page *page, bool release)
{
        int ret;

        lock_page(page);
        ret = split_huge_page(page);
        unlock_page(page);

        if (ret && release)
                put_page(page);

        return ret;
}

static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
                struct address_space *mapping, pgoff_t index, int flags)
{
        struct to_kill *tk;
        unsigned long size = 0;

        list_for_each_entry(tk, to_kill, nd)
                if (tk->size_shift)
                        size = max(size, 1UL << tk->size_shift);

        if (size) {
                /*
                 * Unmap the largest mapping to avoid breaking up device-dax
                 * mappings which are constant size. The actual size of the
                 * mapping being torn down is communicated in siginfo, see
                 * kill_proc()
                 */
                loff_t start = ((loff_t)index << PAGE_SHIFT) & ~(size - 1);

                unmap_mapping_range(mapping, start, size, 0);
        }

        kill_procs(to_kill, flags & MF_MUST_KILL, pfn, flags);
}

/*
 * Only dev_pagemap pages get here, such as fsdax when the filesystem
 * either do not claim or fails to claim a hwpoison event, or devdax.
 * The fsdax pages are initialized per base page, and the devdax pages
 * could be initialized either as base pages, or as compound pages with
 * vmemmap optimization enabled. Devdax is simplistic in its dealing with
 * hwpoison, such that, if a subpage of a compound page is poisoned,
 * simply mark the compound head page is by far sufficient.
 */
static int mf_generic_kill_procs(unsigned long long pfn, int flags,
                struct dev_pagemap *pgmap)
{
        struct folio *folio = pfn_folio(pfn);
        LIST_HEAD(to_kill);
        dax_entry_t cookie;
        int rc = 0;

        /*
         * Prevent the inode from being freed while we are interrogating
         * the address_space, typically this would be handled by
         * lock_page(), but dax pages do not use the page lock. This
         * also prevents changes to the mapping of this pfn until
         * poison signaling is complete.
         */
        cookie = dax_lock_folio(folio);
        if (!cookie)
                return -EBUSY;

        if (hwpoison_filter(&folio->page)) {
                rc = -EOPNOTSUPP;
                goto unlock;
        }

        switch (pgmap->type) {
        case MEMORY_DEVICE_PRIVATE:
        case MEMORY_DEVICE_COHERENT:
                /*
                 * TODO: Handle device pages which may need coordination
                 * with device-side memory.
                 */
                rc = -ENXIO;
                goto unlock;
        default:
                break;
        }

        /*
         * Use this flag as an indication that the dax page has been
         * remapped UC to prevent speculative consumption of poison.
         */
        SetPageHWPoison(&folio->page);

        /*
         * Unlike System-RAM there is no possibility to swap in a
         * different physical page at a given virtual address, so all
         * userspace consumption of ZONE_DEVICE memory necessitates
         * SIGBUS (i.e. MF_MUST_KILL)
         */
        flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
        collect_procs(folio, &folio->page, &to_kill, true);

        unmap_and_kill(&to_kill, pfn, folio->mapping, folio->index, flags);
unlock:
        dax_unlock_folio(folio, cookie);
        return rc;
}

#ifdef CONFIG_FS_DAX
/**
 * mf_dax_kill_procs - Collect and kill processes who are using this file range
 * @mapping:    address_space of the file in use
 * @index:      start pgoff of the range within the file
 * @count:      length of the range, in unit of PAGE_SIZE
 * @mf_flags:   memory failure flags
 */
int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
                unsigned long count, int mf_flags)
{
        LIST_HEAD(to_kill);
        dax_entry_t cookie;
        struct page *page;
        size_t end = index + count;
        bool pre_remove = mf_flags & MF_MEM_PRE_REMOVE;

        mf_flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;

        for (; index < end; index++) {
                page = NULL;
                cookie = dax_lock_mapping_entry(mapping, index, &page);
                if (!cookie)
                        return -EBUSY;
                if (!page)
                        goto unlock;

                if (!pre_remove)
                        SetPageHWPoison(page);

                /*
                 * The pre_remove case is revoking access, the memory is still
                 * good and could theoretically be put back into service.
                 */
                collect_procs_fsdax(page, mapping, index, &to_kill, pre_remove);
                unmap_and_kill(&to_kill, page_to_pfn(page), mapping,
                                index, mf_flags);
unlock:
                dax_unlock_mapping_entry(mapping, index, cookie);
        }
        return 0;
}
EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
#endif /* CONFIG_FS_DAX */

#ifdef CONFIG_HUGETLB_PAGE

/*
 * Struct raw_hwp_page represents information about "raw error page",
 * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
 */
struct raw_hwp_page {
        struct llist_node node;
        struct page *page;
};

static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
{
        return (struct llist_head *)&folio->_hugetlb_hwpoison;
}

bool is_raw_hwpoison_page_in_hugepage(struct page *page)
{
        struct llist_head *raw_hwp_head;
        struct raw_hwp_page *p;
        struct folio *folio = page_folio(page);
        bool ret = false;

        if (!folio_test_hwpoison(folio))
                return false;

        if (!folio_test_hugetlb(folio))
                return PageHWPoison(page);

        /*
         * When RawHwpUnreliable is set, kernel lost track of which subpages
         * are HWPOISON. So return as if ALL subpages are HWPOISONed.
         */
        if (folio_test_hugetlb_raw_hwp_unreliable(folio))
                return true;

        mutex_lock(&mf_mutex);

        raw_hwp_head = raw_hwp_list_head(folio);
        llist_for_each_entry(p, raw_hwp_head->first, node) {
                if (page == p->page) {
                        ret = true;
                        break;
                }
        }

        mutex_unlock(&mf_mutex);

        return ret;
}

static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
{
        struct llist_node *head;
        struct raw_hwp_page *p, *next;
        unsigned long count = 0;

        head = llist_del_all(raw_hwp_list_head(folio));
        llist_for_each_entry_safe(p, next, head, node) {
                if (move_flag)
                        SetPageHWPoison(p->page);
                else
                        num_poisoned_pages_sub(page_to_pfn(p->page), 1);
                kfree(p);
                count++;
        }
        return count;
}

static int folio_set_hugetlb_hwpoison(struct folio *folio, struct page *page)
{
        struct llist_head *head;
        struct raw_hwp_page *raw_hwp;
        struct raw_hwp_page *p;
        int ret = folio_test_set_hwpoison(folio) ? -EHWPOISON : 0;

        /*
         * Once the hwpoison hugepage has lost reliable raw error info,
         * there is little meaning to keep additional error info precisely,
         * so skip to add additional raw error info.
         */
        if (folio_test_hugetlb_raw_hwp_unreliable(folio))
                return -EHWPOISON;
        head = raw_hwp_list_head(folio);
        llist_for_each_entry(p, head->first, node) {
                if (p->page == page)
                        return -EHWPOISON;
        }

        raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
        if (raw_hwp) {
                raw_hwp->page = page;
                llist_add(&raw_hwp->node, head);
                /* the first error event will be counted in action_result(). */
                if (ret)
                        num_poisoned_pages_inc(page_to_pfn(page));
        } else {
                /*
                 * Failed to save raw error info.  We no longer trace all
                 * hwpoisoned subpages, and we need refuse to free/dissolve
                 * this hwpoisoned hugepage.
                 */
                folio_set_hugetlb_raw_hwp_unreliable(folio);
                /*
                 * Once hugetlb_raw_hwp_unreliable is set, raw_hwp_page is not
                 * used any more, so free it.
                 */
                __folio_free_raw_hwp(folio, false);
        }
        return ret;
}

static unsigned long folio_free_raw_hwp(struct folio *folio, bool move_flag)
{
        /*
         * hugetlb_vmemmap_optimized hugepages can't be freed because struct
         * pages for tail pages are required but they don't exist.
         */
        if (move_flag && folio_test_hugetlb_vmemmap_optimized(folio))
                return 0;

        /*
         * hugetlb_raw_hwp_unreliable hugepages shouldn't be unpoisoned by
         * definition.
         */
        if (folio_test_hugetlb_raw_hwp_unreliable(folio))
                return 0;

        return __folio_free_raw_hwp(folio, move_flag);
}

void folio_clear_hugetlb_hwpoison(struct folio *folio)
{
        if (folio_test_hugetlb_raw_hwp_unreliable(folio))
                return;
        if (folio_test_hugetlb_vmemmap_optimized(folio))
                return;
        folio_clear_hwpoison(folio);
        folio_free_raw_hwp(folio, true);
}

/*
 * Called from hugetlb code with hugetlb_lock held.
 *
 * Return values:
 *   0             - free hugepage
 *   1             - in-use hugepage
 *   2             - not a hugepage
 *   -EBUSY        - the hugepage is busy (try to retry)
 *   -EHWPOISON    - the hugepage is already hwpoisoned
 */
int __get_huge_page_for_hwpoison(unsigned long pfn, int flags,
                                 bool *migratable_cleared)
{
        struct page *page = pfn_to_page(pfn);
        struct folio *folio = page_folio(page);
        int ret = 2;    /* fallback to normal page handling */
        bool count_increased = false;

        if (!folio_test_hugetlb(folio))
                goto out;

        if (flags & MF_COUNT_INCREASED) {
                ret = 1;
                count_increased = true;
        } else if (folio_test_hugetlb_freed(folio)) {
                ret = 0;
        } else if (folio_test_hugetlb_migratable(folio)) {
                ret = folio_try_get(folio);
                if (ret)
                        count_increased = true;
        } else {
                ret = -EBUSY;
                if (!(flags & MF_NO_RETRY))
                        goto out;
        }

        if (folio_set_hugetlb_hwpoison(folio, page)) {
                ret = -EHWPOISON;
                goto out;
        }

        /*
         * Clearing hugetlb_migratable for hwpoisoned hugepages to prevent them
         * from being migrated by memory hotremove.
         */
        if (count_increased && folio_test_hugetlb_migratable(folio)) {
                folio_clear_hugetlb_migratable(folio);
                *migratable_cleared = true;
        }

        return ret;
out:
        if (count_increased)
                folio_put(folio);
        return ret;
}

/*
 * Taking refcount of hugetlb pages needs extra care about race conditions
 * with basic operations like hugepage allocation/free/demotion.
 * So some of prechecks for hwpoison (pinning, and testing/setting
 * PageHWPoison) should be done in single hugetlb_lock range.
 */
static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb)
{
        int res;
        struct page *p = pfn_to_page(pfn);
        struct folio *folio;
        unsigned long page_flags;
        bool migratable_cleared = false;

        *hugetlb = 1;
retry:
        res = get_huge_page_for_hwpoison(pfn, flags, &migratable_cleared);
        if (res == 2) { /* fallback to normal page handling */
                *hugetlb = 0;
                return 0;
        } else if (res == -EHWPOISON) {
                pr_err("%#lx: already hardware poisoned\n", pfn);
                if (flags & MF_ACTION_REQUIRED) {
                        folio = page_folio(p);
                        res = kill_accessing_process(current, folio_pfn(folio), flags);
                        action_result(pfn, MF_MSG_ALREADY_POISONED, MF_FAILED);
                }
                return res;
        } else if (res == -EBUSY) {
                if (!(flags & MF_NO_RETRY)) {
                        flags |= MF_NO_RETRY;
                        goto retry;
                }
                return action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
        }

        folio = page_folio(p);
        folio_lock(folio);

        if (hwpoison_filter(p)) {
                folio_clear_hugetlb_hwpoison(folio);
                if (migratable_cleared)
                        folio_set_hugetlb_migratable(folio);
                folio_unlock(folio);
                if (res == 1)
                        folio_put(folio);
                return -EOPNOTSUPP;
        }

        /*
         * Handling free hugepage.  The possible race with hugepage allocation
         * or demotion can be prevented by PageHWPoison flag.
         */
        if (res == 0) {
                folio_unlock(folio);
                if (__page_handle_poison(p) > 0) {
                        page_ref_inc(p);
                        res = MF_RECOVERED;
                } else {
                        res = MF_FAILED;
                }
                return action_result(pfn, MF_MSG_FREE_HUGE, res);
        }

        page_flags = folio->flags;

        if (!hwpoison_user_mappings(folio, p, pfn, flags)) {
                folio_unlock(folio);
                return action_result(pfn, MF_MSG_UNMAP_FAILED, MF_FAILED);
        }

        return identify_page_state(pfn, p, page_flags);
}

#else
static inline int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb)
{
        return 0;
}

static inline unsigned long folio_free_raw_hwp(struct folio *folio, bool flag)
{
        return 0;
}
#endif  /* CONFIG_HUGETLB_PAGE */

/* Drop the extra refcount in case we come from madvise() */
static void put_ref_page(unsigned long pfn, int flags)
{
        if (!(flags & MF_COUNT_INCREASED))
                return;

        put_page(pfn_to_page(pfn));
}

static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
                struct dev_pagemap *pgmap)
{
        int rc = -ENXIO;

        /* device metadata space is not recoverable */
        if (!pgmap_pfn_valid(pgmap, pfn))
                goto out;

        /*
         * Call driver's implementation to handle the memory failure, otherwise
         * fall back to generic handler.
         */
        if (pgmap_has_memory_failure(pgmap)) {
                rc = pgmap->ops->memory_failure(pgmap, pfn, 1, flags);
                /*
                 * Fall back to generic handler too if operation is not
                 * supported inside the driver/device/filesystem.
                 */
                if (rc != -EOPNOTSUPP)
                        goto out;
        }

        rc = mf_generic_kill_procs(pfn, flags, pgmap);
out:
        /* drop pgmap ref acquired in caller */
        put_dev_pagemap(pgmap);
        if (rc != -EOPNOTSUPP)
                action_result(pfn, MF_MSG_DAX, rc ? MF_FAILED : MF_RECOVERED);
        return rc;
}

/*
 * The calling condition is as such: thp split failed, page might have
 * been RDMA pinned, not much can be done for recovery.
 * But a SIGBUS should be delivered with vaddr provided so that the user
 * application has a chance to recover. Also, application processes'
 * election for MCE early killed will be honored.
 */
static void kill_procs_now(struct page *p, unsigned long pfn, int flags,
                                struct folio *folio)
{
        LIST_HEAD(tokill);

        collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
        kill_procs(&tokill, true, pfn, flags);
}

/**
 * memory_failure - Handle memory failure of a page.
 * @pfn: Page Number of the corrupted page
 * @flags: fine tune action taken
 *
 * This function is called by the low level machine check code
 * of an architecture when it detects hardware memory corruption
 * of a page. It tries its best to recover, which includes
 * dropping pages, killing processes etc.
 *
 * The function is primarily of use for corruptions that
 * happen outside the current execution context (e.g. when
 * detected by a background scrubber)
 *
 * Must run in process context (e.g. a work queue) with interrupts
 * enabled and no spinlocks held.
 *
 * Return: 0 for successfully handled the memory error,
 *         -EOPNOTSUPP for hwpoison_filter() filtered the error event,
 *         < 0(except -EOPNOTSUPP) on failure.
 */
int memory_failure(unsigned long pfn, int flags)
{
        struct page *p;
        struct folio *folio;
        struct dev_pagemap *pgmap;
        int res = 0;
        unsigned long page_flags;
        bool retry = true;
        int hugetlb = 0;

        if (!sysctl_memory_failure_recovery)
                panic("Memory failure on page %lx", pfn);

        mutex_lock(&mf_mutex);

        if (!(flags & MF_SW_SIMULATED))
                hw_memory_failure = true;

        p = pfn_to_online_page(pfn);
        if (!p) {
                res = arch_memory_failure(pfn, flags);
                if (res == 0)
                        goto unlock_mutex;

                if (pfn_valid(pfn)) {
                        pgmap = get_dev_pagemap(pfn, NULL);
                        put_ref_page(pfn, flags);
                        if (pgmap) {
                                res = memory_failure_dev_pagemap(pfn, flags,
                                                                 pgmap);
                                goto unlock_mutex;
                        }
                }
                pr_err("%#lx: memory outside kernel control\n", pfn);
                res = -ENXIO;
                goto unlock_mutex;
        }

try_again:
        res = try_memory_failure_hugetlb(pfn, flags, &hugetlb);
        if (hugetlb)
                goto unlock_mutex;

        if (TestSetPageHWPoison(p)) {
                pr_err("%#lx: already hardware poisoned\n", pfn);
                res = -EHWPOISON;
                if (flags & MF_ACTION_REQUIRED)
                        res = kill_accessing_process(current, pfn, flags);
                if (flags & MF_COUNT_INCREASED)
                        put_page(p);
                action_result(pfn, MF_MSG_ALREADY_POISONED, MF_FAILED);
                goto unlock_mutex;
        }

        /*
         * We need/can do nothing about count=0 pages.
         * 1) it's a free page, and therefore in safe hand:
         *    check_new_page() will be the gate keeper.
         * 2) it's part of a non-compound high order page.
         *    Implies some kernel user: cannot stop them from
         *    R/W the page; let's pray that the page has been
         *    used and will be freed some time later.
         * In fact it's dangerous to directly bump up page count from 0,
         * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
         */
        if (!(flags & MF_COUNT_INCREASED)) {
                res = get_hwpoison_page(p, flags);
                if (!res) {
                        if (is_free_buddy_page(p)) {
                                if (take_page_off_buddy(p)) {
                                        page_ref_inc(p);
                                        res = MF_RECOVERED;
                                } else {
                                        /* We lost the race, try again */
                                        if (retry) {
                                                ClearPageHWPoison(p);
                                                retry = false;
                                                goto try_again;
                                        }
                                        res = MF_FAILED;
                                }
                                res = action_result(pfn, MF_MSG_BUDDY, res);
                        } else {
                                res = action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
                        }
                        goto unlock_mutex;
                } else if (res < 0) {
                        res = action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
                        goto unlock_mutex;
                }
        }

        folio = page_folio(p);

        /* filter pages that are protected from hwpoison test by users */
        folio_lock(folio);
        if (hwpoison_filter(p)) {
                ClearPageHWPoison(p);
                folio_unlock(folio);
                folio_put(folio);
                res = -EOPNOTSUPP;
                goto unlock_mutex;
        }
        folio_unlock(folio);

        if (folio_test_large(folio)) {
                /*
                 * The flag must be set after the refcount is bumped
                 * otherwise it may race with THP split.
                 * And the flag can't be set in get_hwpoison_page() since
                 * it is called by soft offline too and it is just called
                 * for !MF_COUNT_INCREASED.  So here seems to be the best
                 * place.
                 *
                 * Don't need care about the above error handling paths for
                 * get_hwpoison_page() since they handle either free page
                 * or unhandlable page.  The refcount is bumped iff the
                 * page is a valid handlable page.
                 */
                folio_set_has_hwpoisoned(folio);
                if (try_to_split_thp_page(p, false) < 0) {
                        res = -EHWPOISON;
                        kill_procs_now(p, pfn, flags, folio);
                        put_page(p);
                        action_result(pfn, MF_MSG_UNSPLIT_THP, MF_FAILED);
                        goto unlock_mutex;
                }
                VM_BUG_ON_PAGE(!page_count(p), p);
                folio = page_folio(p);
        }

        /*
         * We ignore non-LRU pages for good reasons.
         * - PG_locked is only well defined for LRU pages and a few others
         * - to avoid races with __SetPageLocked()
         * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
         * The check (unnecessarily) ignores LRU pages being isolated and
         * walked by the page reclaim code, however that's not a big loss.
         */
        shake_folio(folio);

        folio_lock(folio);

        /*
         * We're only intended to deal with the non-Compound page here.
         * The page cannot become compound pages again as folio has been
         * splited and extra refcnt is held.
         */
        WARN_ON(folio_test_large(folio));

        /*
         * We use page flags to determine what action should be taken, but
         * the flags can be modified by the error containment action.  One
         * example is an mlocked page, where PG_mlocked is cleared by
         * folio_remove_rmap_*() in try_to_unmap_one(). So to determine page
         * status correctly, we save a copy of the page flags at this time.
         */
        page_flags = folio->flags;

        /*
         * __munlock_folio() may clear a writeback folio's LRU flag without
         * the folio lock. We need to wait for writeback completion for this
         * folio or it may trigger a vfs BUG while evicting inode.
         */
        if (!folio_test_lru(folio) && !folio_test_writeback(folio))
                goto identify_page_state;

        /*
         * It's very difficult to mess with pages currently under IO
         * and in many cases impossible, so we just avoid it here.
         */
        folio_wait_writeback(folio);

        /*
         * Now take care of user space mappings.
         * Abort on fail: __filemap_remove_folio() assumes unmapped page.
         */
        if (!hwpoison_user_mappings(folio, p, pfn, flags)) {
                res = action_result(pfn, MF_MSG_UNMAP_FAILED, MF_FAILED);
                goto unlock_page;
        }

        /*
         * Torn down by someone else?
         */
        if (folio_test_lru(folio) && !folio_test_swapcache(folio) &&
            folio->mapping == NULL) {
                res = action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED);
                goto unlock_page;
        }

identify_page_state:
        res = identify_page_state(pfn, p, page_flags);
        mutex_unlock(&mf_mutex);
        return res;
unlock_page:
        folio_unlock(folio);
unlock_mutex:
        mutex_unlock(&mf_mutex);
        return res;
}
EXPORT_SYMBOL_GPL(memory_failure);

#define MEMORY_FAILURE_FIFO_ORDER       4
#define MEMORY_FAILURE_FIFO_SIZE        (1 << MEMORY_FAILURE_FIFO_ORDER)

struct memory_failure_entry {
        unsigned long pfn;
        int flags;
};

struct memory_failure_cpu {
        DECLARE_KFIFO(fifo, struct memory_failure_entry,
                      MEMORY_FAILURE_FIFO_SIZE);
        raw_spinlock_t lock;
        struct work_struct work;
};

static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);

/**
 * memory_failure_queue - Schedule handling memory failure of a page.
 * @pfn: Page Number of the corrupted page
 * @flags: Flags for memory failure handling
 *
 * This function is called by the low level hardware error handler
 * when it detects hardware memory corruption of a page. It schedules
 * the recovering of error page, including dropping pages, killing
 * processes etc.
 *
 * The function is primarily of use for corruptions that
 * happen outside the current execution context (e.g. when
 * detected by a background scrubber)
 *
 * Can run in IRQ context.
 */
void memory_failure_queue(unsigned long pfn, int flags)
{
        struct memory_failure_cpu *mf_cpu;
        unsigned long proc_flags;
        bool buffer_overflow;
        struct memory_failure_entry entry = {
                .pfn =          pfn,
                .flags =        flags,
        };

        mf_cpu = &get_cpu_var(memory_failure_cpu);
        raw_spin_lock_irqsave(&mf_cpu->lock, proc_flags);
        buffer_overflow = !kfifo_put(&mf_cpu->fifo, entry);
        if (!buffer_overflow)
                schedule_work_on(smp_processor_id(), &mf_cpu->work);
        raw_spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
        put_cpu_var(memory_failure_cpu);
        if (buffer_overflow)
                pr_err("buffer overflow when queuing memory failure at %#lx\n",
                       pfn);
}
EXPORT_SYMBOL_GPL(memory_failure_queue);

static void memory_failure_work_func(struct work_struct *work)
{
        struct memory_failure_cpu *mf_cpu;
        struct memory_failure_entry entry = { 0, };
        unsigned long proc_flags;
        int gotten;

        mf_cpu = container_of(work, struct memory_failure_cpu, work);
        for (;;) {
                raw_spin_lock_irqsave(&mf_cpu->lock, proc_flags);
                gotten = kfifo_get(&mf_cpu->fifo, &entry);
                raw_spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
                if (!gotten)
                        break;
                if (entry.flags & MF_SOFT_OFFLINE)
                        soft_offline_page(entry.pfn, entry.flags);
                else
                        memory_failure(entry.pfn, entry.flags);
        }
}

/*
 * Process memory_failure work queued on the specified CPU.
 * Used to avoid return-to-userspace racing with the memory_failure workqueue.
 */
void memory_failure_queue_kick(int cpu)
{
        struct memory_failure_cpu *mf_cpu;

        mf_cpu = &per_cpu(memory_failure_cpu, cpu);
        cancel_work_sync(&mf_cpu->work);
        memory_failure_work_func(&mf_cpu->work);
}

static int __init memory_failure_init(void)
{
        struct memory_failure_cpu *mf_cpu;
        int cpu;

        for_each_possible_cpu(cpu) {
                mf_cpu = &per_cpu(memory_failure_cpu, cpu);
                raw_spin_lock_init(&mf_cpu->lock);
                INIT_KFIFO(mf_cpu->fifo);
                INIT_WORK(&mf_cpu->work, memory_failure_work_func);
        }

        register_sysctl_init("vm", memory_failure_table);

        return 0;
}
core_initcall(memory_failure_init);

#undef pr_fmt
#define pr_fmt(fmt)     "Unpoison: " fmt
#define unpoison_pr_info(fmt, pfn, rs)                  \
({                                                      \
        if (__ratelimit(rs))                            \
                pr_info(fmt, pfn);                      \
})

/**
 * unpoison_memory - Unpoison a previously poisoned page
 * @pfn: Page number of the to be unpoisoned page
 *
 * Software-unpoison a page that has been poisoned by
 * memory_failure() earlier.
 *
 * This is only done on the software-level, so it only works
 * for linux injected failures, not real hardware failures
 *
 * Returns 0 for success, otherwise -errno.
 */
int unpoison_memory(unsigned long pfn)
{
        struct folio *folio;
        struct page *p;
        int ret = -EBUSY, ghp;
        unsigned long count;
        bool huge = false;
        static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
                                        DEFAULT_RATELIMIT_BURST);

        if (!pfn_valid(pfn))
                return -ENXIO;

        p = pfn_to_page(pfn);
        folio = page_folio(p);

        mutex_lock(&mf_mutex);

        if (hw_memory_failure) {
                unpoison_pr_info("%#lx: disabled after HW memory failure\n",
                                 pfn, &unpoison_rs);
                ret = -EOPNOTSUPP;
                goto unlock_mutex;
        }

        if (is_huge_zero_folio(folio)) {
                unpoison_pr_info("%#lx: huge zero page is not supported\n",
                                 pfn, &unpoison_rs);
                ret = -EOPNOTSUPP;
                goto unlock_mutex;
        }

        if (!PageHWPoison(p)) {
                unpoison_pr_info("%#lx: page was already unpoisoned\n",
                                 pfn, &unpoison_rs);
                goto unlock_mutex;
        }

        if (folio_ref_count(folio) > 1) {
                unpoison_pr_info("%#lx: someone grabs the hwpoison page\n",
                                 pfn, &unpoison_rs);
                goto unlock_mutex;
        }

        if (folio_test_slab(folio) || folio_test_pgtable(folio) ||
            folio_test_reserved(folio) || folio_test_offline(folio))
                goto unlock_mutex;

        if (folio_mapped(folio)) {
                unpoison_pr_info("%#lx: someone maps the hwpoison page\n",
                                 pfn, &unpoison_rs);
                goto unlock_mutex;
        }

        if (folio_mapping(folio)) {
                unpoison_pr_info("%#lx: the hwpoison page has non-NULL mapping\n",
                                 pfn, &unpoison_rs);
                goto unlock_mutex;
        }

        ghp = get_hwpoison_page(p, MF_UNPOISON);
        if (!ghp) {
                if (folio_test_hugetlb(folio)) {
                        huge = true;
                        count = folio_free_raw_hwp(folio, false);
                        if (count == 0)
                                goto unlock_mutex;
                }
                ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
        } else if (ghp < 0) {
                if (ghp == -EHWPOISON) {
                        ret = put_page_back_buddy(p) ? 0 : -EBUSY;
                } else {
                        ret = ghp;
                        unpoison_pr_info("%#lx: failed to grab page\n",
                                         pfn, &unpoison_rs);
                }
        } else {
                if (folio_test_hugetlb(folio)) {
                        huge = true;
                        count = folio_free_raw_hwp(folio, false);
                        if (count == 0) {
                                folio_put(folio);
                                goto unlock_mutex;
                        }
                }

                folio_put(folio);
                if (TestClearPageHWPoison(p)) {
                        folio_put(folio);
                        ret = 0;
                }
        }

unlock_mutex:
        mutex_unlock(&mf_mutex);
        if (!ret) {
                if (!huge)
                        num_poisoned_pages_sub(pfn, 1);
                unpoison_pr_info("%#lx: software-unpoisoned page\n",
                                 page_to_pfn(p), &unpoison_rs);
        }
        return ret;
}
EXPORT_SYMBOL(unpoison_memory);

#undef pr_fmt
#define pr_fmt(fmt) "Soft offline: " fmt

/*
 * soft_offline_in_use_page handles hugetlb-pages and non-hugetlb pages.
 * If the page is a non-dirty unmapped page-cache page, it simply invalidates.
 * If the page is mapped, it migrates the contents over.
 */
static int soft_offline_in_use_page(struct page *page)
{
        long ret = 0;
        unsigned long pfn = page_to_pfn(page);
        struct folio *folio = page_folio(page);
        char const *msg_page[] = {"page", "hugepage"};
        bool huge = folio_test_hugetlb(folio);
        bool isolated;
        LIST_HEAD(pagelist);
        struct migration_target_control mtc = {
                .nid = NUMA_NO_NODE,
                .gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
                .reason = MR_MEMORY_FAILURE,
        };

        if (!huge && folio_test_large(folio)) {
                if (try_to_split_thp_page(page, true)) {
                        pr_info("%#lx: thp split failed\n", pfn);
                        return -EBUSY;
                }
                folio = page_folio(page);
        }

        folio_lock(folio);
        if (!huge)
                folio_wait_writeback(folio);
        if (PageHWPoison(page)) {
                folio_unlock(folio);
                folio_put(folio);
                pr_info("%#lx: page already poisoned\n", pfn);
                return 0;
        }

        if (!huge && folio_test_lru(folio) && !folio_test_swapcache(folio))
                /*
                 * Try to invalidate first. This should work for
                 * non dirty unmapped page cache pages.
                 */
                ret = mapping_evict_folio(folio_mapping(folio), folio);
        folio_unlock(folio);

        if (ret) {
                pr_info("%#lx: invalidated\n", pfn);
                page_handle_poison(page, false, true);
                return 0;
        }

        isolated = isolate_folio_to_list(folio, &pagelist);

        /*
         * If we succeed to isolate the folio, we grabbed another refcount on
         * the folio, so we can safely drop the one we got from get_any_page().
         * If we failed to isolate the folio, it means that we cannot go further
         * and we will return an error, so drop the reference we got from
         * get_any_page() as well.
         */
        folio_put(folio);

        if (isolated) {
                ret = migrate_pages(&pagelist, alloc_migration_target, NULL,
                        (unsigned long)&mtc, MIGRATE_SYNC, MR_MEMORY_FAILURE, NULL);
                if (!ret) {
                        bool release = !huge;

                        if (!page_handle_poison(page, huge, release))
                                ret = -EBUSY;
                } else {
                        if (!list_empty(&pagelist))
                                putback_movable_pages(&pagelist);

                        pr_info("%#lx: %s migration failed %ld, type %pGp\n",
                                pfn, msg_page[huge], ret, &page->flags);
                        if (ret > 0)
                                ret = -EBUSY;
                }
        } else {
                pr_info("%#lx: %s isolation failed, page count %d, type %pGp\n",
                        pfn, msg_page[huge], page_count(page), &page->flags);
                ret = -EBUSY;
        }
        return ret;
}

/**
 * soft_offline_page - Soft offline a page.
 * @pfn: pfn to soft-offline
 * @flags: flags. Same as memory_failure().
 *
 * Returns 0 on success,
 *         -EOPNOTSUPP for hwpoison_filter() filtered the error event, or
 *         disabled by /proc/sys/vm/enable_soft_offline,
 *         < 0 otherwise negated errno.
 *
 * Soft offline a page, by migration or invalidation,
 * without killing anything. This is for the case when
 * a page is not corrupted yet (so it's still valid to access),
 * but has had a number of corrected errors and is better taken
 * out.
 *
 * The actual policy on when to do that is maintained by
 * user space.
 *
 * This should never impact any application or cause data loss,
 * however it might take some time.
 *
 * This is not a 100% solution for all memory, but tries to be
 * ``good enough'' for the majority of memory.
 */
int soft_offline_page(unsigned long pfn, int flags)
{
        int ret;
        bool try_again = true;
        struct page *page;

        if (!pfn_valid(pfn)) {
                WARN_ON_ONCE(flags & MF_COUNT_INCREASED);
                return -ENXIO;
        }

        /* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
        page = pfn_to_online_page(pfn);
        if (!page) {
                put_ref_page(pfn, flags);
                return -EIO;
        }

        if (!sysctl_enable_soft_offline) {
                pr_info_once("disabled by /proc/sys/vm/enable_soft_offline\n");
                put_ref_page(pfn, flags);
                return -EOPNOTSUPP;
        }

        mutex_lock(&mf_mutex);

        if (PageHWPoison(page)) {
                pr_info("%#lx: page already poisoned\n", pfn);
                put_ref_page(pfn, flags);
                mutex_unlock(&mf_mutex);
                return 0;
        }

retry:
        get_online_mems();
        ret = get_hwpoison_page(page, flags | MF_SOFT_OFFLINE);
        put_online_mems();

        if (hwpoison_filter(page)) {
                if (ret > 0)
                        put_page(page);

                mutex_unlock(&mf_mutex);
                return -EOPNOTSUPP;
        }

        if (ret > 0) {
                ret = soft_offline_in_use_page(page);
        } else if (ret == 0) {
                if (!page_handle_poison(page, true, false)) {
                        if (try_again) {
                                try_again = false;
                                flags &= ~MF_COUNT_INCREASED;
                                goto retry;
                        }
                        ret = -EBUSY;
                }
        }

        mutex_unlock(&mf_mutex);

        return ret;
}