Re: [PATCH 2/2] vhost-vdpa: fix page pinning leakage in error path (rework)
From: si-wei liu
Date: Thu Nov 05 2020 - 17:40:23 EST
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@xxxxxxxxxx>
---
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;
}