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Date: Tue, 03 Nov 2020 17:08:43 -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 11/3/2020 5:06 PM, si-wei liu wrote:
>
> On 11/3/2020 5:00 AM, 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) {
>>> + 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);
>>
>>
>> I want to know what's wrong with current code.
>>
>> We call vhost_vdpa_unmap() on error which calls
>> vhost_vdpa_iotlb_unmap() that will unpin and reduce the pinned_vm.
> Think about the case where vhost_vdpa_map() fails in the middle after
> making a few successful ones. In the current code, the
> vhost_vdpa_iotlb_unmap() unpins what had been mapped, but does not
> unpin those that have not yet been mapped. These outstanding pinned
> pages will be leaked after leaving the vhost_vdpa_map() function.
Typo: ... leaving the vhost_vdpa_process_iotlb_update() function.
>
> Also, the subtraction accounting at the end of the function is
> incorrect in that case: @npages is deduced by @pinned in each
> iteration. That's why I moved the accounting to vhost_vdpa_map() to be
> symmetric with vhost_vdpa_unmap().
>
>
> -Siwei
>>
>> Thanks
>>
>>
>>> - 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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