Re: [PATCH v3] vhost-vdpa: fix page pinning leakage in error path (rework)

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Nov 05, 2020 at 06:26:33PM -0500, 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@oracle.com>


Not sure which tree this is against, I had to apply this with
minor tweaks. Pls take a look at the vhost tree and
let me know whether it looks ok to you.

> ---
> Changes in v3:
> - Turn explicit last_pfn check to a WARN_ON() (Jason)
> 
> Changes in v2:
> - Drop the reversion patch
> - Fix unhandled page leak towards the end of page_list
> 
>  drivers/vhost/vdpa.c | 80 ++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 62 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index b6d9016..5b13dfd 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);
>  					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 +687,27 @@ static int vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
>  			     map_pfn << PAGE_SHIFT, msg->perm);
>  out:
>  	if (ret) {
> +		if (nchunks) {
> +			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().
> +			 */
> +			WARN_ON(!last_pfn);
> +			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;
>  }
> -- 
> 1.8.3.1