md/raid1: only allocate write behind bio for WriteMostly device

[linux.git] / arch / x86 / mm / fault.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1995  Linus Torvalds
 *  Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
 *  Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
 */
#include <linux/sched.h>                /* test_thread_flag(), ...      */
#include <linux/sched/task_stack.h>     /* task_stack_*(), ...          */
#include <linux/kdebug.h>               /* oops_begin/end, ...          */
#include <linux/extable.h>              /* search_exception_tables      */
#include <linux/memblock.h>             /* max_low_pfn                  */
#include <linux/kfence.h>               /* kfence_handle_page_fault     */
#include <linux/kprobes.h>              /* NOKPROBE_SYMBOL, ...         */
#include <linux/mmiotrace.h>            /* kmmio_handler, ...           */
#include <linux/perf_event.h>           /* perf_sw_event                */
#include <linux/hugetlb.h>              /* hstate_index_to_shift        */
#include <linux/prefetch.h>             /* prefetchw                    */
#include <linux/context_tracking.h>     /* exception_enter(), ...       */
#include <linux/uaccess.h>              /* faulthandler_disabled()      */
#include <linux/efi.h>                  /* efi_crash_gracefully_on_page_fault()*/
#include <linux/mm_types.h>

#include <asm/cpufeature.h>             /* boot_cpu_has, ...            */
#include <asm/traps.h>                  /* dotraplinkage, ...           */
#include <asm/fixmap.h>                 /* VSYSCALL_ADDR                */
#include <asm/vsyscall.h>               /* emulate_vsyscall             */
#include <asm/vm86.h>                   /* struct vm86                  */
#include <asm/mmu_context.h>            /* vma_pkey()                   */
#include <asm/efi.h>                    /* efi_crash_gracefully_on_page_fault()*/
#include <asm/desc.h>                   /* store_idt(), ...             */
#include <asm/cpu_entry_area.h>         /* exception stack              */
#include <asm/pgtable_areas.h>          /* VMALLOC_START, ...           */
#include <asm/kvm_para.h>               /* kvm_handle_async_pf          */
#include <asm/vdso.h>                   /* fixup_vdso_exception()       */

#define CREATE_TRACE_POINTS
#include <asm/trace/exceptions.h>

/*
 * Returns 0 if mmiotrace is disabled, or if the fault is not
 * handled by mmiotrace:
 */
static nokprobe_inline int
kmmio_fault(struct pt_regs *regs, unsigned long addr)
{
        if (unlikely(is_kmmio_active()))
                if (kmmio_handler(regs, addr) == 1)
                        return -1;
        return 0;
}

/*
 * Prefetch quirks:
 *
 * 32-bit mode:
 *
 *   Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 *   Check that here and ignore it.  This is AMD erratum #91.
 *
 * 64-bit mode:
 *
 *   Sometimes the CPU reports invalid exceptions on prefetch.
 *   Check that here and ignore it.
 *
 * Opcode checker based on code by Richard Brunner.
 */
static inline int
check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
                      unsigned char opcode, int *prefetch)
{
        unsigned char instr_hi = opcode & 0xf0;
        unsigned char instr_lo = opcode & 0x0f;

        switch (instr_hi) {
        case 0x20:
        case 0x30:
                /*
                 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
                 * In X86_64 long mode, the CPU will signal invalid
                 * opcode if some of these prefixes are present so
                 * X86_64 will never get here anyway
                 */
                return ((instr_lo & 7) == 0x6);
#ifdef CONFIG_X86_64
        case 0x40:
                /*
                 * In 64-bit mode 0x40..0x4F are valid REX prefixes
                 */
                return (!user_mode(regs) || user_64bit_mode(regs));
#endif
        case 0x60:
                /* 0x64 thru 0x67 are valid prefixes in all modes. */
                return (instr_lo & 0xC) == 0x4;
        case 0xF0:
                /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
                return !instr_lo || (instr_lo>>1) == 1;
        case 0x00:
                /* Prefetch instruction is 0x0F0D or 0x0F18 */
                if (get_kernel_nofault(opcode, instr))
                        return 0;

                *prefetch = (instr_lo == 0xF) &&
                        (opcode == 0x0D || opcode == 0x18);
                return 0;
        default:
                return 0;
        }
}

static bool is_amd_k8_pre_npt(void)
{
        struct cpuinfo_x86 *c = &boot_cpu_data;

        return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) &&
                        c->x86_vendor == X86_VENDOR_AMD &&
                        c->x86 == 0xf && c->x86_model < 0x40);
}

static int
is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
{
        unsigned char *max_instr;
        unsigned char *instr;
        int prefetch = 0;

        /* Erratum #91 affects AMD K8, pre-NPT CPUs */
        if (!is_amd_k8_pre_npt())
                return 0;

        /*
         * If it was a exec (instruction fetch) fault on NX page, then
         * do not ignore the fault:
         */
        if (error_code & X86_PF_INSTR)
                return 0;

        instr = (void *)convert_ip_to_linear(current, regs);
        max_instr = instr + 15;

        /*
         * This code has historically always bailed out if IP points to a
         * not-present page (e.g. due to a race).  No one has ever
         * complained about this.
         */
        pagefault_disable();

        while (instr < max_instr) {
                unsigned char opcode;

                if (user_mode(regs)) {
                        if (get_user(opcode, instr))
                                break;
                } else {
                        if (get_kernel_nofault(opcode, instr))
                                break;
                }

                instr++;

                if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
                        break;
        }

        pagefault_enable();
        return prefetch;
}

DEFINE_SPINLOCK(pgd_lock);
LIST_HEAD(pgd_list);

#ifdef CONFIG_X86_32
static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
        unsigned index = pgd_index(address);
        pgd_t *pgd_k;
        p4d_t *p4d, *p4d_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;

        pgd += index;
        pgd_k = init_mm.pgd + index;

        if (!pgd_present(*pgd_k))
                return NULL;

        /*
         * set_pgd(pgd, *pgd_k); here would be useless on PAE
         * and redundant with the set_pmd() on non-PAE. As would
         * set_p4d/set_pud.
         */
        p4d = p4d_offset(pgd, address);
        p4d_k = p4d_offset(pgd_k, address);
        if (!p4d_present(*p4d_k))
                return NULL;

        pud = pud_offset(p4d, address);
        pud_k = pud_offset(p4d_k, address);
        if (!pud_present(*pud_k))
                return NULL;

        pmd = pmd_offset(pud, address);
        pmd_k = pmd_offset(pud_k, address);

        if (pmd_present(*pmd) != pmd_present(*pmd_k))
                set_pmd(pmd, *pmd_k);

        if (!pmd_present(*pmd_k))
                return NULL;
        else
                BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));

        return pmd_k;
}

/*
 *   Handle a fault on the vmalloc or module mapping area
 *
 *   This is needed because there is a race condition between the time
 *   when the vmalloc mapping code updates the PMD to the point in time
 *   where it synchronizes this update with the other page-tables in the
 *   system.
 *
 *   In this race window another thread/CPU can map an area on the same
 *   PMD, finds it already present and does not synchronize it with the
 *   rest of the system yet. As a result v[mz]alloc might return areas
 *   which are not mapped in every page-table in the system, causing an
 *   unhandled page-fault when they are accessed.
 */
static noinline int vmalloc_fault(unsigned long address)
{
        unsigned long pgd_paddr;
        pmd_t *pmd_k;
        pte_t *pte_k;

        /* Make sure we are in vmalloc area: */
        if (!(address >= VMALLOC_START && address < VMALLOC_END))
                return -1;

        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Do _not_ use "current" here. We might be inside
         * an interrupt in the middle of a task switch..
         */
        pgd_paddr = read_cr3_pa();
        pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
        if (!pmd_k)
                return -1;

        if (pmd_large(*pmd_k))
                return 0;

        pte_k = pte_offset_kernel(pmd_k, address);
        if (!pte_present(*pte_k))
                return -1;

        return 0;
}
NOKPROBE_SYMBOL(vmalloc_fault);

void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
{
        unsigned long addr;

        for (addr = start & PMD_MASK;
             addr >= TASK_SIZE_MAX && addr < VMALLOC_END;
             addr += PMD_SIZE) {
                struct page *page;

                spin_lock(&pgd_lock);
                list_for_each_entry(page, &pgd_list, lru) {
                        spinlock_t *pgt_lock;

                        /* the pgt_lock only for Xen */
                        pgt_lock = &pgd_page_get_mm(page)->page_table_lock;

                        spin_lock(pgt_lock);
                        vmalloc_sync_one(page_address(page), addr);
                        spin_unlock(pgt_lock);
                }
                spin_unlock(&pgd_lock);
        }
}

static bool low_pfn(unsigned long pfn)
{
        return pfn < max_low_pfn;
}

static void dump_pagetable(unsigned long address)
{
        pgd_t *base = __va(read_cr3_pa());
        pgd_t *pgd = &base[pgd_index(address)];
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

#ifdef CONFIG_X86_PAE
        pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
        if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
                goto out;
#define pr_pde pr_cont
#else
#define pr_pde pr_info
#endif
        p4d = p4d_offset(pgd, address);
        pud = pud_offset(p4d, address);
        pmd = pmd_offset(pud, address);
        pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
#undef pr_pde

        /*
         * We must not directly access the pte in the highpte
         * case if the page table is located in highmem.
         * And let's rather not kmap-atomic the pte, just in case
         * it's allocated already:
         */
        if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
                goto out;

        pte = pte_offset_kernel(pmd, address);
        pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
out:
        pr_cont("\n");
}

#else /* CONFIG_X86_64: */

#ifdef CONFIG_CPU_SUP_AMD
static const char errata93_warning[] =
KERN_ERR 
"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
"******* Working around it, but it may cause SEGVs or burn power.\n"
"******* Please consider a BIOS update.\n"
"******* Disabling USB legacy in the BIOS may also help.\n";
#endif

static int bad_address(void *p)
{
        unsigned long dummy;

        return get_kernel_nofault(dummy, (unsigned long *)p);
}

static void dump_pagetable(unsigned long address)
{
        pgd_t *base = __va(read_cr3_pa());
        pgd_t *pgd = base + pgd_index(address);
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        if (bad_address(pgd))
                goto bad;

        pr_info("PGD %lx ", pgd_val(*pgd));

        if (!pgd_present(*pgd))
                goto out;

        p4d = p4d_offset(pgd, address);
        if (bad_address(p4d))
                goto bad;

        pr_cont("P4D %lx ", p4d_val(*p4d));
        if (!p4d_present(*p4d) || p4d_large(*p4d))
                goto out;

        pud = pud_offset(p4d, address);
        if (bad_address(pud))
                goto bad;

        pr_cont("PUD %lx ", pud_val(*pud));
        if (!pud_present(*pud) || pud_large(*pud))
                goto out;

        pmd = pmd_offset(pud, address);
        if (bad_address(pmd))
                goto bad;

        pr_cont("PMD %lx ", pmd_val(*pmd));
        if (!pmd_present(*pmd) || pmd_large(*pmd))
                goto out;

        pte = pte_offset_kernel(pmd, address);
        if (bad_address(pte))
                goto bad;

        pr_cont("PTE %lx", pte_val(*pte));
out:
        pr_cont("\n");
        return;
bad:
        pr_info("BAD\n");
}

#endif /* CONFIG_X86_64 */

/*
 * Workaround for K8 erratum #93 & buggy BIOS.
 *
 * BIOS SMM functions are required to use a specific workaround
 * to avoid corruption of the 64bit RIP register on C stepping K8.
 *
 * A lot of BIOS that didn't get tested properly miss this.
 *
 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
 * Try to work around it here.
 *
 * Note we only handle faults in kernel here.
 * Does nothing on 32-bit.
 */
static int is_errata93(struct pt_regs *regs, unsigned long address)
{
#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
        if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
            || boot_cpu_data.x86 != 0xf)
                return 0;

        if (user_mode(regs))
                return 0;

        if (address != regs->ip)
                return 0;

        if ((address >> 32) != 0)
                return 0;

        address |= 0xffffffffUL << 32;
        if ((address >= (u64)_stext && address <= (u64)_etext) ||
            (address >= MODULES_VADDR && address <= MODULES_END)) {
                printk_once(errata93_warning);
                regs->ip = address;
                return 1;
        }
#endif
        return 0;
}

/*
 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
 * to illegal addresses >4GB.
 *
 * We catch this in the page fault handler because these addresses
 * are not reachable. Just detect this case and return.  Any code
 * segment in LDT is compatibility mode.
 */
static int is_errata100(struct pt_regs *regs, unsigned long address)
{
#ifdef CONFIG_X86_64
        if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
                return 1;
#endif
        return 0;
}

/* Pentium F0 0F C7 C8 bug workaround: */
static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code,
                       unsigned long address)
{
#ifdef CONFIG_X86_F00F_BUG
        if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) &&
            idt_is_f00f_address(address)) {
                handle_invalid_op(regs);
                return 1;
        }
#endif
        return 0;
}

static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
{
        u32 offset = (index >> 3) * sizeof(struct desc_struct);
        unsigned long addr;
        struct ldttss_desc desc;

        if (index == 0) {
                pr_alert("%s: NULL\n", name);
                return;
        }

        if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
                pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
                return;
        }

        if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset),
                              sizeof(struct ldttss_desc))) {
                pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
                         name, index);
                return;
        }

        addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
#ifdef CONFIG_X86_64
        addr |= ((u64)desc.base3 << 32);
#endif
        pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
                 name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
}

static void
show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
        if (!oops_may_print())
                return;

        if (error_code & X86_PF_INSTR) {
                unsigned int level;
                pgd_t *pgd;
                pte_t *pte;

                pgd = __va(read_cr3_pa());
                pgd += pgd_index(address);

                pte = lookup_address_in_pgd(pgd, address, &level);

                if (pte && pte_present(*pte) && !pte_exec(*pte))
                        pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
                                from_kuid(&init_user_ns, current_uid()));
                if (pte && pte_present(*pte) && pte_exec(*pte) &&
                                (pgd_flags(*pgd) & _PAGE_USER) &&
                                (__read_cr4() & X86_CR4_SMEP))
                        pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
                                from_kuid(&init_user_ns, current_uid()));
        }

        if (address < PAGE_SIZE && !user_mode(regs))
                pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
                        (void *)address);
        else
                pr_alert("BUG: unable to handle page fault for address: %px\n",
                        (void *)address);

        pr_alert("#PF: %s %s in %s mode\n",
                 (error_code & X86_PF_USER)  ? "user" : "supervisor",
                 (error_code & X86_PF_INSTR) ? "instruction fetch" :
                 (error_code & X86_PF_WRITE) ? "write access" :
                                               "read access",
                             user_mode(regs) ? "user" : "kernel");
        pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
                 !(error_code & X86_PF_PROT) ? "not-present page" :
                 (error_code & X86_PF_RSVD)  ? "reserved bit violation" :
                 (error_code & X86_PF_PK)    ? "protection keys violation" :
                                               "permissions violation");

        if (!(error_code & X86_PF_USER) && user_mode(regs)) {
                struct desc_ptr idt, gdt;
                u16 ldtr, tr;

                /*
                 * This can happen for quite a few reasons.  The more obvious
                 * ones are faults accessing the GDT, or LDT.  Perhaps
                 * surprisingly, if the CPU tries to deliver a benign or
                 * contributory exception from user code and gets a page fault
                 * during delivery, the page fault can be delivered as though
                 * it originated directly from user code.  This could happen
                 * due to wrong permissions on the IDT, GDT, LDT, TSS, or
                 * kernel or IST stack.
                 */
                store_idt(&idt);

                /* Usable even on Xen PV -- it's just slow. */
                native_store_gdt(&gdt);

                pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
                         idt.address, idt.size, gdt.address, gdt.size);

                store_ldt(ldtr);
                show_ldttss(&gdt, "LDTR", ldtr);

                store_tr(tr);
                show_ldttss(&gdt, "TR", tr);
        }

        dump_pagetable(address);
}

static noinline void
pgtable_bad(struct pt_regs *regs, unsigned long error_code,
            unsigned long address)
{
        struct task_struct *tsk;
        unsigned long flags;
        int sig;

        flags = oops_begin();
        tsk = current;
        sig = SIGKILL;

        printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
               tsk->comm, address);
        dump_pagetable(address);

        if (__die("Bad pagetable", regs, error_code))
                sig = 0;

        oops_end(flags, regs, sig);
}

static void sanitize_error_code(unsigned long address,
                                unsigned long *error_code)
{
        /*
         * To avoid leaking information about the kernel page
         * table layout, pretend that user-mode accesses to
         * kernel addresses are always protection faults.
         *
         * NB: This means that failed vsyscalls with vsyscall=none
         * will have the PROT bit.  This doesn't leak any
         * information and does not appear to cause any problems.
         */
        if (address >= TASK_SIZE_MAX)
                *error_code |= X86_PF_PROT;
}

static void set_signal_archinfo(unsigned long address,
                                unsigned long error_code)
{
        struct task_struct *tsk = current;

        tsk->thread.trap_nr = X86_TRAP_PF;
        tsk->thread.error_code = error_code | X86_PF_USER;
        tsk->thread.cr2 = address;
}

static noinline void
page_fault_oops(struct pt_regs *regs, unsigned long error_code,
                unsigned long address)
{
        unsigned long flags;
        int sig;

        if (user_mode(regs)) {
                /*
                 * Implicit kernel access from user mode?  Skip the stack
                 * overflow and EFI special cases.
                 */
                goto oops;
        }

#ifdef CONFIG_VMAP_STACK
        /*
         * Stack overflow?  During boot, we can fault near the initial
         * stack in the direct map, but that's not an overflow -- check
         * that we're in vmalloc space to avoid this.
         */
        if (is_vmalloc_addr((void *)address) &&
            (((unsigned long)current->stack - 1 - address < PAGE_SIZE) ||
             address - ((unsigned long)current->stack + THREAD_SIZE) < PAGE_SIZE)) {
                unsigned long stack = __this_cpu_ist_top_va(DF) - sizeof(void *);
                /*
                 * We're likely to be running with very little stack space
                 * left.  It's plausible that we'd hit this condition but
                 * double-fault even before we get this far, in which case
                 * we're fine: the double-fault handler will deal with it.
                 *
                 * We don't want to make it all the way into the oops code
                 * and then double-fault, though, because we're likely to
                 * break the console driver and lose most of the stack dump.
                 */
                asm volatile ("movq %[stack], %%rsp\n\t"
                              "call handle_stack_overflow\n\t"
                              "1: jmp 1b"
                              : ASM_CALL_CONSTRAINT
                              : "D" ("kernel stack overflow (page fault)"),
                                "S" (regs), "d" (address),
                                [stack] "rm" (stack));
                unreachable();
        }
#endif

        /*
         * Buggy firmware could access regions which might page fault.  If
         * this happens, EFI has a special OOPS path that will try to
         * avoid hanging the system.
         */
        if (IS_ENABLED(CONFIG_EFI))
                efi_crash_gracefully_on_page_fault(address);

        /* Only not-present faults should be handled by KFENCE. */
        if (!(error_code & X86_PF_PROT) &&
            kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs))
                return;

oops:
        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice:
         */
        flags = oops_begin();

        show_fault_oops(regs, error_code, address);

        if (task_stack_end_corrupted(current))
                printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");

        sig = SIGKILL;
        if (__die("Oops", regs, error_code))
                sig = 0;

        /* Executive summary in case the body of the oops scrolled away */
        printk(KERN_DEFAULT "CR2: %016lx\n", address);

        oops_end(flags, regs, sig);
}

static noinline void
kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
                         unsigned long address, int signal, int si_code,
                         u32 pkey)
{
        WARN_ON_ONCE(user_mode(regs));

        /* Are we prepared to handle this kernel fault? */
        if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) {
                /*
                 * Any interrupt that takes a fault gets the fixup. This makes
                 * the below recursive fault logic only apply to a faults from
                 * task context.
                 */
                if (in_interrupt())
                        return;

                /*
                 * Per the above we're !in_interrupt(), aka. task context.
                 *
                 * In this case we need to make sure we're not recursively
                 * faulting through the emulate_vsyscall() logic.
                 */
                if (current->thread.sig_on_uaccess_err && signal) {
                        sanitize_error_code(address, &error_code);

                        set_signal_archinfo(address, error_code);

                        if (si_code == SEGV_PKUERR) {
                                force_sig_pkuerr((void __user *)address, pkey);
                        } else {
                                /* XXX: hwpoison faults will set the wrong code. */
                                force_sig_fault(signal, si_code, (void __user *)address);
                        }
                }

                /*
                 * Barring that, we can do the fixup and be happy.
                 */
                return;
        }

        /*
         * AMD erratum #91 manifests as a spurious page fault on a PREFETCH
         * instruction.
         */
        if (is_prefetch(regs, error_code, address))
                return;

        page_fault_oops(regs, error_code, address);
}

/*
 * Print out info about fatal segfaults, if the show_unhandled_signals
 * sysctl is set:
 */
static inline void
show_signal_msg(struct pt_regs *regs, unsigned long error_code,
                unsigned long address, struct task_struct *tsk)
{
        const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;

        if (!unhandled_signal(tsk, SIGSEGV))
                return;

        if (!printk_ratelimit())
                return;

        printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
                loglvl, tsk->comm, task_pid_nr(tsk), address,
                (void *)regs->ip, (void *)regs->sp, error_code);

        print_vma_addr(KERN_CONT " in ", regs->ip);

        printk(KERN_CONT "\n");

        show_opcodes(regs, loglvl);
}

/*
 * The (legacy) vsyscall page is the long page in the kernel portion
 * of the address space that has user-accessible permissions.
 */
static bool is_vsyscall_vaddr(unsigned long vaddr)
{
        return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
}

static void
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
                       unsigned long address, u32 pkey, int si_code)
{
        struct task_struct *tsk = current;

        if (!user_mode(regs)) {
                kernelmode_fixup_or_oops(regs, error_code, address,
                                         SIGSEGV, si_code, pkey);
                return;
        }

        if (!(error_code & X86_PF_USER)) {
                /* Implicit user access to kernel memory -- just oops */
                page_fault_oops(regs, error_code, address);
                return;
        }

        /*
         * User mode accesses just cause a SIGSEGV.
         * It's possible to have interrupts off here:
         */
        local_irq_enable();

        /*
         * Valid to do another page fault here because this one came
         * from user space:
         */
        if (is_prefetch(regs, error_code, address))
                return;

        if (is_errata100(regs, address))
                return;

        sanitize_error_code(address, &error_code);

        if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
                return;

        if (likely(show_unhandled_signals))
                show_signal_msg(regs, error_code, address, tsk);

        set_signal_archinfo(address, error_code);

        if (si_code == SEGV_PKUERR)
                force_sig_pkuerr((void __user *)address, pkey);
        else
                force_sig_fault(SIGSEGV, si_code, (void __user *)address);

        local_irq_disable();
}

static noinline void
bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
                     unsigned long address)
{
        __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
}

static void
__bad_area(struct pt_regs *regs, unsigned long error_code,
           unsigned long address, u32 pkey, int si_code)
{
        struct mm_struct *mm = current->mm;
        /*
         * Something tried to access memory that isn't in our memory map..
         * Fix it, but check if it's kernel or user first..
         */
        mmap_read_unlock(mm);

        __bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
}

static noinline void
bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
{
        __bad_area(regs, error_code, address, 0, SEGV_MAPERR);
}

static inline bool bad_area_access_from_pkeys(unsigned long error_code,
                struct vm_area_struct *vma)
{
        /* This code is always called on the current mm */
        bool foreign = false;

        if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
                return false;
        if (error_code & X86_PF_PK)
                return true;
        /* this checks permission keys on the VMA: */
        if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
                                       (error_code & X86_PF_INSTR), foreign))
                return true;
        return false;
}

static noinline void
bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
                      unsigned long address, struct vm_area_struct *vma)
{
        /*
         * This OSPKE check is not strictly necessary at runtime.
         * But, doing it this way allows compiler optimizations
         * if pkeys are compiled out.
         */
        if (bad_area_access_from_pkeys(error_code, vma)) {
                /*
                 * A protection key fault means that the PKRU value did not allow
                 * access to some PTE.  Userspace can figure out what PKRU was
                 * from the XSAVE state.  This function captures the pkey from
                 * the vma and passes it to userspace so userspace can discover
                 * which protection key was set on the PTE.
                 *
                 * If we get here, we know that the hardware signaled a X86_PF_PK
                 * fault and that there was a VMA once we got in the fault
                 * handler.  It does *not* guarantee that the VMA we find here
                 * was the one that we faulted on.
                 *
                 * 1. T1   : mprotect_key(foo, PAGE_SIZE, pkey=4);
                 * 2. T1   : set PKRU to deny access to pkey=4, touches page
                 * 3. T1   : faults...
                 * 4.    T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
                 * 5. T1   : enters fault handler, takes mmap_lock, etc...
                 * 6. T1   : reaches here, sees vma_pkey(vma)=5, when we really
                 *           faulted on a pte with its pkey=4.
                 */
                u32 pkey = vma_pkey(vma);

                __bad_area(regs, error_code, address, pkey, SEGV_PKUERR);
        } else {
                __bad_area(regs, error_code, address, 0, SEGV_ACCERR);
        }
}

static void
do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
          vm_fault_t fault)
{
        /* Kernel mode? Handle exceptions or die: */
        if (!user_mode(regs)) {
                kernelmode_fixup_or_oops(regs, error_code, address,
                                         SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
                return;
        }

        /* User-space => ok to do another page fault: */
        if (is_prefetch(regs, error_code, address))
                return;

        sanitize_error_code(address, &error_code);

        if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
                return;

        set_signal_archinfo(address, error_code);

#ifdef CONFIG_MEMORY_FAILURE
        if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
                struct task_struct *tsk = current;
                unsigned lsb = 0;

                pr_err(
        "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
                        tsk->comm, tsk->pid, address);
                if (fault & VM_FAULT_HWPOISON_LARGE)
                        lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
                if (fault & VM_FAULT_HWPOISON)
                        lsb = PAGE_SHIFT;
                force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
                return;
        }
#endif
        force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
}

static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
{
        if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
                return 0;

        if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
                return 0;

        return 1;
}

/*
 * Handle a spurious fault caused by a stale TLB entry.
 *
 * This allows us to lazily refresh the TLB when increasing the
 * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
 * eagerly is very expensive since that implies doing a full
 * cross-processor TLB flush, even if no stale TLB entries exist
 * on other processors.
 *
 * Spurious faults may only occur if the TLB contains an entry with
 * fewer permission than the page table entry.  Non-present (P = 0)
 * and reserved bit (R = 1) faults are never spurious.
 *
 * There are no security implications to leaving a stale TLB when
 * increasing the permissions on a page.
 *
 * Returns non-zero if a spurious fault was handled, zero otherwise.
 *
 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
 * (Optional Invalidation).
 */
static noinline int
spurious_kernel_fault(unsigned long error_code, unsigned long address)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;
        int ret;

        /*
         * Only writes to RO or instruction fetches from NX may cause
         * spurious faults.
         *
         * These could be from user or supervisor accesses but the TLB
         * is only lazily flushed after a kernel mapping protection
         * change, so user accesses are not expected to cause spurious
         * faults.
         */
        if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
            error_code != (X86_PF_INSTR | X86_PF_PROT))
                return 0;

        pgd = init_mm.pgd + pgd_index(address);
        if (!pgd_present(*pgd))
                return 0;

        p4d = p4d_offset(pgd, address);
        if (!p4d_present(*p4d))
                return 0;

        if (p4d_large(*p4d))
                return spurious_kernel_fault_check(error_code, (pte_t *) p4d);

        pud = pud_offset(p4d, address);
        if (!pud_present(*pud))
                return 0;

        if (pud_large(*pud))
                return spurious_kernel_fault_check(error_code, (pte_t *) pud);

        pmd = pmd_offset(pud, address);
        if (!pmd_present(*pmd))
                return 0;

        if (pmd_large(*pmd))
                return spurious_kernel_fault_check(error_code, (pte_t *) pmd);

        pte = pte_offset_kernel(pmd, address);
        if (!pte_present(*pte))
                return 0;

        ret = spurious_kernel_fault_check(error_code, pte);
        if (!ret)
                return 0;

        /*
         * Make sure we have permissions in PMD.
         * If not, then there's a bug in the page tables:
         */
        ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
        WARN_ONCE(!ret, "PMD has incorrect permission bits\n");

        return ret;
}
NOKPROBE_SYMBOL(spurious_kernel_fault);

int show_unhandled_signals = 1;

static inline int
access_error(unsigned long error_code, struct vm_area_struct *vma)
{
        /* This is only called for the current mm, so: */
        bool foreign = false;

        /*
         * Read or write was blocked by protection keys.  This is
         * always an unconditional error and can never result in
         * a follow-up action to resolve the fault, like a COW.
         */
        if (error_code & X86_PF_PK)
                return 1;

        /*
         * SGX hardware blocked the access.  This usually happens
         * when the enclave memory contents have been destroyed, like
         * after a suspend/resume cycle. In any case, the kernel can't
         * fix the cause of the fault.  Handle the fault as an access
         * error even in cases where no actual access violation
         * occurred.  This allows userspace to rebuild the enclave in
         * response to the signal.
         */
        if (unlikely(error_code & X86_PF_SGX))
                return 1;

        /*
         * Make sure to check the VMA so that we do not perform
         * faults just to hit a X86_PF_PK as soon as we fill in a
         * page.
         */
        if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
                                       (error_code & X86_PF_INSTR), foreign))
                return 1;

        if (error_code & X86_PF_WRITE) {
                /* write, present and write, not present: */
                if (unlikely(!(vma->vm_flags & VM_WRITE)))
                        return 1;
                return 0;
        }

        /* read, present: */
        if (unlikely(error_code & X86_PF_PROT))
                return 1;

        /* read, not present: */
        if (unlikely(!vma_is_accessible(vma)))
                return 1;

        return 0;
}

bool fault_in_kernel_space(unsigned long address)
{
        /*
         * On 64-bit systems, the vsyscall page is at an address above
         * TASK_SIZE_MAX, but is not considered part of the kernel
         * address space.
         */
        if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
                return false;

        return address >= TASK_SIZE_MAX;
}

/*
 * Called for all faults where 'address' is part of the kernel address
 * space.  Might get called for faults that originate from *code* that
 * ran in userspace or the kernel.
 */
static void
do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
                   unsigned long address)
{
        /*
         * Protection keys exceptions only happen on user pages.  We
         * have no user pages in the kernel portion of the address
         * space, so do not expect them here.
         */
        WARN_ON_ONCE(hw_error_code & X86_PF_PK);

#ifdef CONFIG_X86_32
        /*
         * We can fault-in kernel-space virtual memory on-demand. The
         * 'reference' page table is init_mm.pgd.
         *
         * NOTE! We MUST NOT take any locks for this case. We may
         * be in an interrupt or a critical region, and should
         * only copy the information from the master page table,
         * nothing more.
         *
         * Before doing this on-demand faulting, ensure that the
         * fault is not any of the following:
         * 1. A fault on a PTE with a reserved bit set.
         * 2. A fault caused by a user-mode access.  (Do not demand-
         *    fault kernel memory due to user-mode accesses).
         * 3. A fault caused by a page-level protection violation.
         *    (A demand fault would be on a non-present page which
         *     would have X86_PF_PROT==0).
         *
         * This is only needed to close a race condition on x86-32 in
         * the vmalloc mapping/unmapping code. See the comment above
         * vmalloc_fault() for details. On x86-64 the race does not
         * exist as the vmalloc mappings don't need to be synchronized
         * there.
         */
        if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
                if (vmalloc_fault(address) >= 0)
                        return;
        }
#endif

        if (is_f00f_bug(regs, hw_error_code, address))
                return;

        /* Was the fault spurious, caused by lazy TLB invalidation? */
        if (spurious_kernel_fault(hw_error_code, address))
                return;

        /* kprobes don't want to hook the spurious faults: */
        if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
                return;

        /*
         * Note, despite being a "bad area", there are quite a few
         * acceptable reasons to get here, such as erratum fixups
         * and handling kernel code that can fault, like get_user().
         *
         * Don't take the mm semaphore here. If we fixup a prefetch
         * fault we could otherwise deadlock:
         */
        bad_area_nosemaphore(regs, hw_error_code, address);
}
NOKPROBE_SYMBOL(do_kern_addr_fault);

/*
 * Handle faults in the user portion of the address space.  Nothing in here
 * should check X86_PF_USER without a specific justification: for almost
 * all purposes, we should treat a normal kernel access to user memory
 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction.
 * The one exception is AC flag handling, which is, per the x86
 * architecture, special for WRUSS.
 */
static inline
void do_user_addr_fault(struct pt_regs *regs,
                        unsigned long error_code,
                        unsigned long address)
{
        struct vm_area_struct *vma;
        struct task_struct *tsk;
        struct mm_struct *mm;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_DEFAULT;

        tsk = current;
        mm = tsk->mm;

        if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
                /*
                 * Whoops, this is kernel mode code trying to execute from
                 * user memory.  Unless this is AMD erratum #93, which
                 * corrupts RIP such that it looks like a user address,
                 * this is unrecoverable.  Don't even try to look up the
                 * VMA or look for extable entries.
                 */
                if (is_errata93(regs, address))
                        return;

                page_fault_oops(regs, error_code, address);
                return;
        }

        /* kprobes don't want to hook the spurious faults: */
        if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
                return;

        /*
         * Reserved bits are never expected to be set on
         * entries in the user portion of the page tables.
         */
        if (unlikely(error_code & X86_PF_RSVD))
                pgtable_bad(regs, error_code, address);

        /*
         * If SMAP is on, check for invalid kernel (supervisor) access to user
         * pages in the user address space.  The odd case here is WRUSS,
         * which, according to the preliminary documentation, does not respect
         * SMAP and will have the USER bit set so, in all cases, SMAP
         * enforcement appears to be consistent with the USER bit.
         */
        if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
                     !(error_code & X86_PF_USER) &&
                     !(regs->flags & X86_EFLAGS_AC))) {
                /*
                 * No extable entry here.  This was a kernel access to an
                 * invalid pointer.  get_kernel_nofault() will not get here.
                 */
                page_fault_oops(regs, error_code, address);
                return;
        }

        /*
         * If we're in an interrupt, have no user context or are running
         * in a region with pagefaults disabled then we must not take the fault
         */
        if (unlikely(faulthandler_disabled() || !mm)) {
                bad_area_nosemaphore(regs, error_code, address);
                return;
        }

        /*
         * It's safe to allow irq's after cr2 has been saved and the
         * vmalloc fault has been handled.
         *
         * User-mode registers count as a user access even for any
         * potential system fault or CPU buglet:
         */
        if (user_mode(regs)) {
                local_irq_enable();
                flags |= FAULT_FLAG_USER;
        } else {
                if (regs->flags & X86_EFLAGS_IF)
                        local_irq_enable();
        }

        perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

        if (error_code & X86_PF_WRITE)
                flags |= FAULT_FLAG_WRITE;
        if (error_code & X86_PF_INSTR)
                flags |= FAULT_FLAG_INSTRUCTION;

#ifdef CONFIG_X86_64
        /*
         * Faults in the vsyscall page might need emulation.  The
         * vsyscall page is at a high address (>PAGE_OFFSET), but is
         * considered to be part of the user address space.
         *
         * The vsyscall page does not have a "real" VMA, so do this
         * emulation before we go searching for VMAs.
         *
         * PKRU never rejects instruction fetches, so we don't need
         * to consider the PF_PK bit.
         */
        if (is_vsyscall_vaddr(address)) {
                if (emulate_vsyscall(error_code, regs, address))
                        return;
        }
#endif

        /*
         * Kernel-mode access to the user address space should only occur
         * on well-defined single instructions listed in the exception
         * tables.  But, an erroneous kernel fault occurring outside one of
         * those areas which also holds mmap_lock might deadlock attempting
         * to validate the fault against the address space.
         *
         * Only do the expensive exception table search when we might be at
         * risk of a deadlock.  This happens if we
         * 1. Failed to acquire mmap_lock, and
         * 2. The access did not originate in userspace.
         */
        if (unlikely(!mmap_read_trylock(mm))) {
                if (!user_mode(regs) && !search_exception_tables(regs->ip)) {
                        /*
                         * Fault from code in kernel from
                         * which we do not expect faults.
                         */
                        bad_area_nosemaphore(regs, error_code, address);
                        return;
                }
retry:
                mmap_read_lock(mm);
        } else {
                /*
                 * The above down_read_trylock() might have succeeded in
                 * which case we'll have missed the might_sleep() from
                 * down_read():
                 */
                might_sleep();
        }

        vma = find_vma(mm, address);
        if (unlikely(!vma)) {
                bad_area(regs, error_code, address);
                return;
        }
        if (likely(vma->vm_start <= address))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
                bad_area(regs, error_code, address);
                return;
        }
        if (unlikely(expand_stack(vma, address))) {
                bad_area(regs, error_code, address);
                return;
        }

        /*
         * Ok, we have a good vm_area for this memory access, so
         * we can handle it..
         */
good_area:
        if (unlikely(access_error(error_code, vma))) {
                bad_area_access_error(regs, error_code, address, vma);
                return;
        }

        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.  Since we never set FAULT_FLAG_RETRY_NOWAIT, if
         * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked.
         *
         * Note that handle_userfault() may also release and reacquire mmap_lock
         * (and not return with VM_FAULT_RETRY), when returning to userland to
         * repeat the page fault later with a VM_FAULT_NOPAGE retval
         * (potentially after handling any pending signal during the return to
         * userland). The return to userland is identified whenever
         * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
         */
        fault = handle_mm_fault(vma, address, flags, regs);

        if (fault_signal_pending(fault, regs)) {
                /*
                 * Quick path to respond to signals.  The core mm code
                 * has unlocked the mm for us if we get here.
                 */
                if (!user_mode(regs))
                        kernelmode_fixup_or_oops(regs, error_code, address,
                                                 SIGBUS, BUS_ADRERR,
                                                 ARCH_DEFAULT_PKEY);
                return;
        }

        /*
         * If we need to retry the mmap_lock has already been released,
         * and if there is a fatal signal pending there is no guarantee
         * that we made any progress. Handle this case first.
         */
        if (unlikely((fault & VM_FAULT_RETRY) &&
                     (flags & FAULT_FLAG_ALLOW_RETRY))) {
                flags |= FAULT_FLAG_TRIED;
                goto retry;
        }

        mmap_read_unlock(mm);
        if (likely(!(fault & VM_FAULT_ERROR)))
                return;

        if (fatal_signal_pending(current) && !user_mode(regs)) {
                kernelmode_fixup_or_oops(regs, error_code, address,
                                         0, 0, ARCH_DEFAULT_PKEY);
                return;
        }

        if (fault & VM_FAULT_OOM) {
                /* Kernel mode? Handle exceptions or die: */
                if (!user_mode(regs)) {
                        kernelmode_fixup_or_oops(regs, error_code, address,
                                                 SIGSEGV, SEGV_MAPERR,
                                                 ARCH_DEFAULT_PKEY);
                        return;
                }

                /*
                 * We ran out of memory, call the OOM killer, and return the
                 * userspace (which will retry the fault, or kill us if we got
                 * oom-killed):
                 */
                pagefault_out_of_memory();
        } else {
                if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
                             VM_FAULT_HWPOISON_LARGE))
                        do_sigbus(regs, error_code, address, fault);
                else if (fault & VM_FAULT_SIGSEGV)
                        bad_area_nosemaphore(regs, error_code, address);
                else
                        BUG();
        }
}
NOKPROBE_SYMBOL(do_user_addr_fault);

static __always_inline void
trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
                         unsigned long address)
{
        if (!trace_pagefault_enabled())
                return;

        if (user_mode(regs))
                trace_page_fault_user(address, regs, error_code);
        else
                trace_page_fault_kernel(address, regs, error_code);
}

static __always_inline void
handle_page_fault(struct pt_regs *regs, unsigned long error_code,
                              unsigned long address)
{
        trace_page_fault_entries(regs, error_code, address);

        if (unlikely(kmmio_fault(regs, address)))
                return;

        /* Was the fault on kernel-controlled part of the address space? */
        if (unlikely(fault_in_kernel_space(address))) {
                do_kern_addr_fault(regs, error_code, address);
        } else {
                do_user_addr_fault(regs, error_code, address);
                /*
                 * User address page fault handling might have reenabled
                 * interrupts. Fixing up all potential exit points of
                 * do_user_addr_fault() and its leaf functions is just not
                 * doable w/o creating an unholy mess or turning the code
                 * upside down.
                 */
                local_irq_disable();
        }
}

DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
{
        unsigned long address = read_cr2();
        irqentry_state_t state;

        prefetchw(&current->mm->mmap_lock);

        /*
         * KVM uses #PF vector to deliver 'page not present' events to guests
         * (asynchronous page fault mechanism). The event happens when a
         * userspace task is trying to access some valid (from guest's point of
         * view) memory which is not currently mapped by the host (e.g. the
         * memory is swapped out). Note, the corresponding "page ready" event
         * which is injected when the memory becomes available, is delivered via
         * an interrupt mechanism and not a #PF exception
         * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
         *
         * We are relying on the interrupted context being sane (valid RSP,
         * relevant locks not held, etc.), which is fine as long as the
         * interrupted context had IF=1.  We are also relying on the KVM
         * async pf type field and CR2 being read consistently instead of
         * getting values from real and async page faults mixed up.
         *
         * Fingers crossed.
         *
         * The async #PF handling code takes care of idtentry handling
         * itself.
         */
        if (kvm_handle_async_pf(regs, (u32)address))
                return;

        /*
         * Entry handling for valid #PF from kernel mode is slightly
         * different: RCU is already watching and rcu_irq_enter() must not
         * be invoked because a kernel fault on a user space address might
         * sleep.
         *
         * In case the fault hit a RCU idle region the conditional entry
         * code reenabled RCU to avoid subsequent wreckage which helps
         * debuggability.
         */
        state = irqentry_enter(regs);

        instrumentation_begin();
        handle_page_fault(regs, error_code, address);
        instrumentation_end();

        irqentry_exit(regs, state);
}