drivers/xen/privcmd-buf.c

   1 // SPDX-License-Identifier: GPL-2.0 OR MIT
   2
   3 /******************************************************************************
   4  * privcmd-buf.c
   5  *
   6  * Mmap of hypercall buffers.
   7  *
   8  * Copyright (c) 2018 Juergen Gross
   9  */
  10
  11 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
  12
  13 #include <linux/kernel.h>
  14 #include <linux/module.h>
  15 #include <linux/list.h>
  16 #include <linux/miscdevice.h>
  17 #include <linux/mm.h>
  18 #include <linux/slab.h>
  19
  20 #include "privcmd.h"
  21
  22 MODULE_DESCRIPTION("Xen Mmap of hypercall buffers");
  23 MODULE_LICENSE("GPL");
  24
  25 struct privcmd_buf_private {
  26         struct mutex lock;
  27         struct list_head list;
  28 };
  29
  30 struct privcmd_buf_vma_private {
  31         struct privcmd_buf_private *file_priv;
  32         struct list_head list;
  33         unsigned int users;
  34         unsigned int n_pages;
  35         struct page *pages[];
  36 };
  37
  38 static int privcmd_buf_open(struct inode *ino, struct file *file)
  39 {
  40         struct privcmd_buf_private *file_priv;
  41
  42         file_priv = kzalloc(sizeof(*file_priv), GFP_KERNEL);
  43         if (!file_priv)
  44                 return -ENOMEM;
  45
  46         mutex_init(&file_priv->lock);
  47         INIT_LIST_HEAD(&file_priv->list);
  48
  49         file->private_data = file_priv;
  50
  51         return 0;
  52 }
  53
  54 static void privcmd_buf_vmapriv_free(struct privcmd_buf_vma_private *vma_priv)
  55 {
  56         unsigned int i;
  57
  58         list_del(&vma_priv->list);
  59
  60         for (i = 0; i < vma_priv->n_pages; i++)
  61                 __free_page(vma_priv->pages[i]);
  62
  63         kfree(vma_priv);
  64 }
  65
  66 static int privcmd_buf_release(struct inode *ino, struct file *file)
  67 {
  68         struct privcmd_buf_private *file_priv = file->private_data;
  69         struct privcmd_buf_vma_private *vma_priv;
  70
  71         mutex_lock(&file_priv->lock);
  72
  73         while (!list_empty(&file_priv->list)) {
  74                 vma_priv = list_first_entry(&file_priv->list,
  75                                             struct privcmd_buf_vma_private,
  76                                             list);
  77                 privcmd_buf_vmapriv_free(vma_priv);
  78         }
  79
  80         mutex_unlock(&file_priv->lock);
  81
  82         kfree(file_priv);
  83
  84         return 0;
  85 }
  86
  87 static void privcmd_buf_vma_open(struct vm_area_struct *vma)
  88 {
  89         struct privcmd_buf_vma_private *vma_priv = vma->vm_private_data;
  90
  91         if (!vma_priv)
  92                 return;
  93
  94         mutex_lock(&vma_priv->file_priv->lock);
  95         vma_priv->users++;
  96         mutex_unlock(&vma_priv->file_priv->lock);
  97 }
  98
  99 static void privcmd_buf_vma_close(struct vm_area_struct *vma)
 100 {
 101         struct privcmd_buf_vma_private *vma_priv = vma->vm_private_data;
 102         struct privcmd_buf_private *file_priv;
 103
 104         if (!vma_priv)
 105                 return;
 106
 107         file_priv = vma_priv->file_priv;
 108
 109         mutex_lock(&file_priv->lock);
 110
 111         vma_priv->users--;
 112         if (!vma_priv->users)
 113                 privcmd_buf_vmapriv_free(vma_priv);
 114
 115         mutex_unlock(&file_priv->lock);
 116 }
 117
 118 static vm_fault_t privcmd_buf_vma_fault(struct vm_fault *vmf)
 119 {
 120         pr_debug("fault: vma=%p %lx-%lx, pgoff=%lx, uv=%p\n",
 121                  vmf->vma, vmf->vma->vm_start, vmf->vma->vm_end,
 122                  vmf->pgoff, (void *)vmf->address);
 123
 124         return VM_FAULT_SIGBUS;
 125 }
 126
 127 static const struct vm_operations_struct privcmd_buf_vm_ops = {
 128         .open = privcmd_buf_vma_open,
 129         .close = privcmd_buf_vma_close,
 130         .fault = privcmd_buf_vma_fault,
 131 };
 132
 133 static int privcmd_buf_mmap(struct file *file, struct vm_area_struct *vma)
 134 {
 135         struct privcmd_buf_private *file_priv = file->private_data;
 136         struct privcmd_buf_vma_private *vma_priv;
 137         unsigned long count = vma_pages(vma);
 138         unsigned int i;
 139         int ret = 0;
 140
 141         if (!(vma->vm_flags & VM_SHARED))
 142                 return -EINVAL;
 143
 144         vma_priv = kzalloc(struct_size(vma_priv, pages, count), GFP_KERNEL);
 145         if (!vma_priv)
 146                 return -ENOMEM;
 147
 148         for (i = 0; i < count; i++) {
 149                 vma_priv->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
 150                 if (!vma_priv->pages[i])
 151                         break;
 152                 vma_priv->n_pages++;
 153         }
 154
 155         mutex_lock(&file_priv->lock);
 156
 157         vma_priv->file_priv = file_priv;
 158         vma_priv->users = 1;
 159
 160         vm_flags_set(vma, VM_IO | VM_DONTEXPAND);
 161         vma->vm_ops = &privcmd_buf_vm_ops;
 162         vma->vm_private_data = vma_priv;
 163
 164         list_add(&vma_priv->list, &file_priv->list);
 165
 166         if (vma_priv->n_pages != count)
 167                 ret = -ENOMEM;
 168         else
 169                 ret = vm_map_pages_zero(vma, vma_priv->pages,
 170                                                 vma_priv->n_pages);
 171
 172         if (ret)
 173                 privcmd_buf_vmapriv_free(vma_priv);
 174
 175         mutex_unlock(&file_priv->lock);
 176
 177         return ret;
 178 }
 179
 180 const struct file_operations xen_privcmdbuf_fops = {
 181         .owner = THIS_MODULE,
 182         .open = privcmd_buf_open,
 183         .release = privcmd_buf_release,
 184         .mmap = privcmd_buf_mmap,
 185 };
 186 EXPORT_SYMBOL_GPL(xen_privcmdbuf_fops);
 187
 188 struct miscdevice xen_privcmdbuf_dev = {
 189         .minor = MISC_DYNAMIC_MINOR,
 190         .name = "xen/hypercall",
 191         .fops = &xen_privcmdbuf_fops,
 192 };