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Date: Thu, 05 Nov 2020 14:40:12 -0800
From: si-wei liu <si-wei.liu@...cle.com>
To: Jason Wang <jasowang@...hat.com>, mst@...hat.com,
lingshan.zhu@...el.com
CC: joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
linux-kernel@...r.kernel.org,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 2/2] vhost-vdpa: fix page pinning leakage in error path
(rework)
On 11/4/2020 7:12 PM, Jason Wang wrote:
>
> On 2020/11/5 上午7:40, si-wei liu wrote:
>>
>> On 11/3/2020 6:42 PM, Jason Wang wrote:
>>>
>>> On 2020/10/30 下午3:45, 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@...cle.com>
>>>> ---
>>>> drivers/vhost/vdpa.c | 64
>>>> +++++++++++++++++++++++++++++++++++++---------------
>>>> 1 file changed, 46 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>>>> index b6d9016..8da8558 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 +611,64 @@ 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)
>>>> 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 +676,22 @@ static int
>>>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>>>> map_pfn << PAGE_SHIFT, msg->perm);
>>>> out:
>>>> if (ret) {
>>>> + if (nchunks && last_pfn) {
>>>
>>>
>>> Can we decrease npages where you did "nchunks++" then we can check
>>> npages here instead?
>> Hmmm, I am not sure I get what you want... @nchunks gets reset to 0
>> whenever a certain range of pinned pages is successfully mapped. The
>> conditional (when nchunks is non-zero) here indicates if there's any
>> _outstanding_ pinned page that has to clean up in the error handling
>> path. While the decrement of @npages may not occur when resetting the
>> @nchunks counter, rendering incorrect cleanup in the error path.
>
>
> Yes, I meant e can decrease npages where you did "nchunks++". Anyhow,
> it's just a optimization to avoid a local variable which is not a must.
To me that opportunity doesn't exist. @nchunks and @npages track
different kind of things. @npages is not interchangeable to represent
all possible error cases.
-Siwei
>
>
>>
>> BTW while reviewing it I got noticed of an error in my code. There
>> might be still page pinning leak from wherever the vhost_vdpa_map()
>> error occurs towards the end of page_list. I will post a v2 to fix this.
>>
>
> Sure, will review.
>
> Thanks
>
>
>> Regards,
>> -Siwei
>>
>> --- a/drivers/vhost/vdpa.c
>> +++ b/drivers/vhost/vdpa.c
>> @@ -656,8 +656,19 @@ static int
>> vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>> ret = vhost_vdpa_map(v, iova, csize,
>> map_pfn <<
>> PAGE_SHIFT,
>> msg->perm);
>> - if (ret)
>> + 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);
>> goto out;
>> + }
>>
>> map_pfn = this_pfn;
>> iova += csize;
>>
>>
>>
>>>
>>> Thanks
>>>
>>>
>>>> + unsigned long pfn;
>>>> +
>>>> + /*
>>>> + * Unpin the outstanding pages which are unmapped.
>>>> + * Mapped pages are accounted in vdpa_map(), thus
>>>> + * 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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