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Message-ID: <5FA33C06.6010000@oracle.com>
Date: Wed, 04 Nov 2020 15:40:54 -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 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.
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.
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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