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SubjectRe: [PATCH v2] vhost-vdpa: fix page pinning leakage in error path (rework)
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On 2020/11/6 上午6:57, si-wei liu wrote:
>
> On 11/4/2020 7:26 PM, Jason Wang wrote:
>>
>> On 2020/11/5 上午7:33, 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.
>>>
>>> The memory usage for bookkeeping pinned pages is reverted
>>> to what it was before: only one single free page is needed.
>>> This helps reduce the host memory demand for VM with a large
>>> amount of memory, or in the situation where host is running
>>> short of free memory.
>>>
>>> Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
>>> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
>>> ---
>>> Changes in v2:
>>> - Drop the reversion patch
>>> - Fix unhandled page leak towards the end of page_list
>>>
>>>   drivers/vhost/vdpa.c | 79
>>> ++++++++++++++++++++++++++++++++++++++++------------
>>>   1 file changed, 61 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>>> index b6d9016..e112854 100644
>>> --- a/drivers/vhost/vdpa.c
>>> +++ b/drivers/vhost/vdpa.c
>>> @@ -560,6 +560,8 @@ static int vhost_vdpa_map(struct vhost_vdpa *v,
>>>         if (r)
>>>           vhost_iotlb_del_range(dev->iotlb, iova, iova + size - 1);
>>> +    else
>>> +        atomic64_add(size >> PAGE_SHIFT, &dev->mm->pinned_vm);
>>>         return r;
>>>   }
>>> @@ -591,14 +593,16 @@ static int
>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>>>       unsigned long list_size = PAGE_SIZE / sizeof(struct page *);
>>>       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 lock_limit, sz2pin, nchunks, i;
>>>       u64 iova = msg->iova;
>>> +    long pinned;
>>>       int ret = 0;
>>>         if (vhost_iotlb_itree_first(iotlb, msg->iova,
>>>                       msg->iova + msg->size - 1))
>>>           return -EEXIST;
>>>   +    /* Limit the use of memory for bookkeeping */
>>>       page_list = (struct page **) __get_free_page(GFP_KERNEL);
>>>       if (!page_list)
>>>           return -ENOMEM;
>>> @@ -607,52 +611,75 @@ static int
>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>>>           gup_flags |= FOLL_WRITE;
>>>         npages = PAGE_ALIGN(msg->size + (iova & ~PAGE_MASK)) >>
>>> PAGE_SHIFT;
>>> -    if (!npages)
>>> -        return -EINVAL;
>>> +    if (!npages) {
>>> +        ret = -EINVAL;
>>> +        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;
>>> +    nchunks = 0;
>>>         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)
>>> +        sz2pin = min_t(unsigned long, npages, list_size);
>>> +        pinned = pin_user_pages(cur_base, sz2pin,
>>> +                    gup_flags, page_list, NULL);
>>> +        if (sz2pin != pinned) {
>>> +            if (pinned < 0) {
>>> +                ret = pinned;
>>> +            } else {
>>> +                unpin_user_pages(page_list, pinned);
>>> +                ret = -ENOMEM;
>>> +            }
>>>               goto out;
>>> +        }
>>> +        nchunks++;
>>>             if (!last_pfn)
>>>               map_pfn = page_to_pfn(page_list[0]);
>>>   -        for (i = 0; i < ret; i++) {
>>> +        for (i = 0; i < pinned; 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))
>>> +                ret = vhost_vdpa_map(v, iova, csize,
>>> +                             map_pfn << PAGE_SHIFT,
>>> +                             msg->perm);
>>> +                if (ret) {
>>> +                    /*
>>> +                     * Unpin the pages that are left unmapped
>>> +                     * from this point on in the current
>>> +                     * page_list. The remaining outstanding
>>> +                     * ones which may stride across several
>>> +                     * chunks will be covered in the common
>>> +                     * error path subsequently.
>>> +                     */
>>> +                    unpin_user_pages(&page_list[i],
>>> +                             pinned - i);
>>
>>
>> Can we simply do last_pfn = this_pfn here?
> Nope. They are not contiguous segments of memory. Noted the
> conditional (this_pfn != last_pfn + 1) being held here.


Right.


>
>>
>>
>>>                       goto out;
>>> +                }
>>> +
>>>                   map_pfn = this_pfn;
>>>                   iova += csize;
>>> +                nchunks = 0;
>>>               }
>>>                 last_pfn = this_pfn;
>>>           }
>>>   -        cur_base += ret << PAGE_SHIFT;
>>> -        npages -= ret;
>>> +        cur_base += pinned << PAGE_SHIFT;
>>> +        npages -= pinned;
>>>       }
>>>         /* Pin the rest chunk */
>>> @@ -660,10 +687,26 @@ static int
>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>>>                    map_pfn << PAGE_SHIFT, msg->perm);
>>>   out:
>>>       if (ret) {
>>> +        if (nchunks && last_pfn) {
>>
>>
>> Any reason for checking last_pfn here?
>>
>> Note that we did:
>>
>> +        nchunks++;
>>
>>          if (!last_pfn)
>>              map_pfn = page_to_pfn(page_list[0]);
> It's for explicit coding to make sure this common error path can be
> reused no matter if last_pfn has a sane value assigned or not. I can
> change it to an implicit WARN_ON() if need be.


Just to make sure I understand. A question, when will we get nchunks !=
0 but last_pfn == 0?

Thanks


> Thanks,
> -Siwei
>
>>
>>
>> Thanks
>>
>>
>>> +            unsigned long pfn;
>>> +
>>> +            /*
>>> +             * Unpin the outstanding pages which are yet to be
>>> +             * mapped but haven't due to vdpa_map() or
>>> +             * pin_user_pages() failure.
>>> +             *
>>> +             * Mapped pages are accounted in vdpa_map(), hence
>>> +             * the corresponding unpinning will be handled by
>>> +             * vdpa_unmap().
>>> +             */
>>> +            for (pfn = map_pfn; pfn <= last_pfn; pfn++)
>>> +                unpin_user_page(pfn_to_page(pfn));
>>> +        }
>>>           vhost_vdpa_unmap(v, msg->iova, msg->size);
>>> -        atomic64_sub(npages, &dev->mm->pinned_vm);
>>>       }
>>> +unlock:
>>>       mmap_read_unlock(dev->mm);
>>> +free:
>>>       free_page((unsigned long)page_list);
>>>       return ret;
>>>   }
>>
>

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