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![Juergen Gross](/assets/img/avatar_default.png)
Currently the size of hypercall buffers allocated via
/dev/xen/hypercall is limited to a default of 64 memory pages. For live
migration of guests this might be too small as the page dirty bitmask
needs to be sized according to the size of the guest. This means
migrating a 8GB sized guest is already exhausting the default buffer
size for the dirty bitmap.
There is no sensible way to set a sane limit, so just remove it
completely. The device node's usage is limited to root anyway, so there
is no additional DOS scenario added by allowing unlimited buffers.
While at it make the error path for the -ENOMEM case a little bit
cleaner by setting n_pages to the number of successfully allocated
pages instead of the target size.
Fixes: c51b3c639e
("xen: add new hypercall buffer mapping device")
Cc: <stable@vger.kernel.org> #4.18
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
196 lines
4.2 KiB
C
196 lines
4.2 KiB
C
// SPDX-License-Identifier: GPL-2.0 OR MIT
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/******************************************************************************
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* privcmd-buf.c
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*
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* Mmap of hypercall buffers.
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*
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* Copyright (c) 2018 Juergen Gross
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*/
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#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/list.h>
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#include <linux/miscdevice.h>
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#include <linux/mm.h>
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#include <linux/slab.h>
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#include "privcmd.h"
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MODULE_LICENSE("GPL");
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struct privcmd_buf_private {
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struct mutex lock;
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struct list_head list;
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};
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struct privcmd_buf_vma_private {
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struct privcmd_buf_private *file_priv;
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struct list_head list;
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unsigned int users;
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unsigned int n_pages;
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struct page *pages[];
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};
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static int privcmd_buf_open(struct inode *ino, struct file *file)
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{
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struct privcmd_buf_private *file_priv;
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file_priv = kzalloc(sizeof(*file_priv), GFP_KERNEL);
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if (!file_priv)
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return -ENOMEM;
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mutex_init(&file_priv->lock);
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INIT_LIST_HEAD(&file_priv->list);
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file->private_data = file_priv;
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return 0;
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}
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static void privcmd_buf_vmapriv_free(struct privcmd_buf_vma_private *vma_priv)
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{
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unsigned int i;
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list_del(&vma_priv->list);
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for (i = 0; i < vma_priv->n_pages; i++)
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__free_page(vma_priv->pages[i]);
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kfree(vma_priv);
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}
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static int privcmd_buf_release(struct inode *ino, struct file *file)
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{
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struct privcmd_buf_private *file_priv = file->private_data;
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struct privcmd_buf_vma_private *vma_priv;
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mutex_lock(&file_priv->lock);
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while (!list_empty(&file_priv->list)) {
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vma_priv = list_first_entry(&file_priv->list,
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struct privcmd_buf_vma_private,
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list);
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privcmd_buf_vmapriv_free(vma_priv);
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}
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mutex_unlock(&file_priv->lock);
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kfree(file_priv);
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return 0;
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}
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static void privcmd_buf_vma_open(struct vm_area_struct *vma)
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{
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struct privcmd_buf_vma_private *vma_priv = vma->vm_private_data;
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if (!vma_priv)
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return;
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mutex_lock(&vma_priv->file_priv->lock);
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vma_priv->users++;
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mutex_unlock(&vma_priv->file_priv->lock);
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}
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static void privcmd_buf_vma_close(struct vm_area_struct *vma)
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{
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struct privcmd_buf_vma_private *vma_priv = vma->vm_private_data;
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struct privcmd_buf_private *file_priv;
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if (!vma_priv)
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return;
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file_priv = vma_priv->file_priv;
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mutex_lock(&file_priv->lock);
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vma_priv->users--;
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if (!vma_priv->users)
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privcmd_buf_vmapriv_free(vma_priv);
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mutex_unlock(&file_priv->lock);
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}
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static vm_fault_t privcmd_buf_vma_fault(struct vm_fault *vmf)
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{
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pr_debug("fault: vma=%p %lx-%lx, pgoff=%lx, uv=%p\n",
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vmf->vma, vmf->vma->vm_start, vmf->vma->vm_end,
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vmf->pgoff, (void *)vmf->address);
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return VM_FAULT_SIGBUS;
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}
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static const struct vm_operations_struct privcmd_buf_vm_ops = {
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.open = privcmd_buf_vma_open,
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.close = privcmd_buf_vma_close,
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.fault = privcmd_buf_vma_fault,
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};
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static int privcmd_buf_mmap(struct file *file, struct vm_area_struct *vma)
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{
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struct privcmd_buf_private *file_priv = file->private_data;
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struct privcmd_buf_vma_private *vma_priv;
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unsigned long count = vma_pages(vma);
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unsigned int i;
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int ret = 0;
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if (!(vma->vm_flags & VM_SHARED))
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return -EINVAL;
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vma_priv = kzalloc(sizeof(*vma_priv) + count * sizeof(void *),
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GFP_KERNEL);
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if (!vma_priv)
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return -ENOMEM;
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for (i = 0; i < count; i++) {
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vma_priv->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
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if (!vma_priv->pages[i])
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break;
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vma_priv->n_pages++;
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}
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mutex_lock(&file_priv->lock);
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vma_priv->file_priv = file_priv;
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vma_priv->users = 1;
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vma->vm_flags |= VM_IO | VM_DONTEXPAND;
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vma->vm_ops = &privcmd_buf_vm_ops;
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vma->vm_private_data = vma_priv;
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list_add(&vma_priv->list, &file_priv->list);
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if (vma_priv->n_pages != count)
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ret = -ENOMEM;
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else
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for (i = 0; i < vma_priv->n_pages; i++) {
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ret = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
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vma_priv->pages[i]);
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if (ret)
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break;
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}
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if (ret)
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privcmd_buf_vmapriv_free(vma_priv);
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mutex_unlock(&file_priv->lock);
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return ret;
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}
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const struct file_operations xen_privcmdbuf_fops = {
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.owner = THIS_MODULE,
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.open = privcmd_buf_open,
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.release = privcmd_buf_release,
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.mmap = privcmd_buf_mmap,
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};
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EXPORT_SYMBOL_GPL(xen_privcmdbuf_fops);
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struct miscdevice xen_privcmdbuf_dev = {
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.minor = MISC_DYNAMIC_MINOR,
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.name = "xen/hypercall",
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.fops = &xen_privcmdbuf_fops,
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};
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