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SubjectRe: [PATCH] vhost-vdpa: fix page pinning leakage in error path
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On 2020/10/2 上午4:23, Si-Wei Liu wrote:
> Pinned pages are not properly accounted particularly when
> mapping error occurs on IOTLB update. Clean up dangling
> pinned pages for the error path. As the inflight pinned
> pages, specifically for memory region that strides across
> multiple chunks, would need more than one free page for
> book keeping and accounting. For simplicity, pin pages
> for all memory in the IOVA range in one go rather than
> have multiple pin_user_pages calls to make up the entire
> region. This way it's easier to track and account the
> pages already mapped, particularly for clean-up in the
> error path.
>
> Fixes: 20453a45fb06 ("vhost: introduce vDPA-based backend")
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> ---
> drivers/vhost/vdpa.c | 121 +++++++++++++++++++++++++++++++--------------------
> 1 file changed, 73 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 796fe97..abc4aa2 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -565,6 +565,8 @@ static int vhost_vdpa_map(struct vhost_vdpa *v,
> perm_to_iommu_flags(perm));
> }
>
> + if (r)
> + vhost_iotlb_del_range(dev->iotlb, iova, iova + size - 1);
> return r;
> }


Please use a separate patch for this fix.


>
> @@ -592,21 +594,19 @@ static int vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
> struct vhost_dev *dev = &v->vdev;
> struct vhost_iotlb *iotlb = dev->iotlb;
> struct page **page_list;
> - unsigned long list_size = PAGE_SIZE / sizeof(struct page *);
> + struct vm_area_struct **vmas;
> unsigned int gup_flags = FOLL_LONGTERM;
> - unsigned long npages, cur_base, map_pfn, last_pfn = 0;
> - unsigned long locked, lock_limit, pinned, i;
> + unsigned long map_pfn, last_pfn = 0;
> + unsigned long npages, lock_limit;
> + unsigned long i, nmap = 0;
> u64 iova = msg->iova;
> + long pinned;
> int ret = 0;
>
> if (vhost_iotlb_itree_first(iotlb, msg->iova,
> msg->iova + msg->size - 1))
> return -EEXIST;
>
> - page_list = (struct page **) __get_free_page(GFP_KERNEL);
> - if (!page_list)
> - return -ENOMEM;
> -
> if (msg->perm & VHOST_ACCESS_WO)
> gup_flags |= FOLL_WRITE;
>
> @@ -614,61 +614,86 @@ static int vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
> if (!npages)
> return -EINVAL;
>
> + page_list = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
> + vmas = kvmalloc_array(npages, sizeof(struct vm_area_struct *),
> + GFP_KERNEL);
> + if (!page_list || !vmas) {
> + ret = -ENOMEM;
> + goto free;
> + }
> +
> mmap_read_lock(dev->mm);
>
> - locked = atomic64_add_return(npages, &dev->mm->pinned_vm);
> lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> -
> - if (locked > lock_limit) {
> + if (npages + atomic64_read(&dev->mm->pinned_vm) > lock_limit) {
> ret = -ENOMEM;
> - goto out;
> + goto unlock;
> }
>
> - cur_base = msg->uaddr & PAGE_MASK;
> - iova &= PAGE_MASK;
> + pinned = pin_user_pages(msg->uaddr & PAGE_MASK, npages, gup_flags,
> + page_list, vmas);
> + if (npages != pinned) {
> + if (pinned < 0) {
> + ret = pinned;
> + } else {
> + unpin_user_pages(page_list, pinned);
> + ret = -ENOMEM;
> + }
> + goto unlock;
> + }
>
> - while (npages) {
> - pinned = min_t(unsigned long, npages, list_size);
> - ret = pin_user_pages(cur_base, pinned,
> - gup_flags, page_list, NULL);
> - if (ret != pinned)
> - goto out;
> -
> - if (!last_pfn)
> - map_pfn = page_to_pfn(page_list[0]);
> -
> - for (i = 0; i < ret; i++) {
> - unsigned long this_pfn = page_to_pfn(page_list[i]);
> - u64 csize;
> -
> - if (last_pfn && (this_pfn != last_pfn + 1)) {
> - /* Pin a contiguous chunk of memory */
> - csize = (last_pfn - map_pfn + 1) << PAGE_SHIFT;
> - if (vhost_vdpa_map(v, iova, csize,
> - map_pfn << PAGE_SHIFT,
> - msg->perm))
> - goto out;
> - map_pfn = this_pfn;
> - iova += csize;
> + iova &= PAGE_MASK;
> + map_pfn = page_to_pfn(page_list[0]);
> +
> + /* One more iteration to avoid extra vdpa_map() call out of loop. */
> + for (i = 0; i <= npages; i++) {
> + unsigned long this_pfn;
> + u64 csize;
> +
> + /* The last chunk may have no valid PFN next to it */
> + this_pfn = i < npages ? page_to_pfn(page_list[i]) : -1UL;
> +
> + if (last_pfn && (this_pfn == -1UL ||
> + this_pfn != last_pfn + 1)) {
> + /* Pin a contiguous chunk of memory */
> + csize = last_pfn - map_pfn + 1;
> + ret = vhost_vdpa_map(v, iova, csize << PAGE_SHIFT,
> + map_pfn << PAGE_SHIFT,
> + msg->perm);
> + if (ret) {
> + /*
> + * Unpin the rest chunks of memory on the
> + * flight with no corresponding vdpa_map()
> + * calls having been made yet. On the other
> + * hand, vdpa_unmap() in the failure path
> + * is in charge of accounting the number of
> + * pinned pages for its own.
> + * This asymmetrical pattern of accounting
> + * is for efficiency to pin all pages at
> + * once, while there is no other callsite
> + * of vdpa_map() than here above.
> + */
> + unpin_user_pages(&page_list[nmap],
> + npages - nmap);
> + goto out;
> }
> -
> - last_pfn = this_pfn;
> + atomic64_add(csize, &dev->mm->pinned_vm);
> + nmap += csize;
> + iova += csize << PAGE_SHIFT;
> + map_pfn = this_pfn;
> }
> -
> - cur_base += ret << PAGE_SHIFT;
> - npages -= ret;
> + last_pfn = this_pfn;
> }
>
> - /* Pin the rest chunk */
> - ret = vhost_vdpa_map(v, iova, (last_pfn - map_pfn + 1) << PAGE_SHIFT,
> - map_pfn << PAGE_SHIFT, msg->perm);
> + WARN_ON(nmap != npages);
> out:
> - if (ret) {
> + if (ret)
> vhost_vdpa_unmap(v, msg->iova, msg->size);
> - atomic64_sub(npages, &dev->mm->pinned_vm);
> - }
> +unlock:
> mmap_read_unlock(dev->mm);
> - free_page((unsigned long)page_list);
> +free:
> + kvfree(vmas);
> + kvfree(page_list);
> return ret;
> }


This looks like a rework, so I'd suggest to use use another patch for
this part.

(I was on vacation, so the reply would be slow)

Thanks


>

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