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Date: Thu, 05 Nov 2020 14:57:06 -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 v2] vhost-vdpa: fix page pinning leakage in error path
(rework)
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@...cle.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.
>
>
>> 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.
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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