Virtualization - Aug 2023 - [PATCH v2] vhost: Allow null msg.size on VHOST_IOTLB_INVALIDATE

Commit e2ae38cf3d91 ("vhost: fix hung thread due to erroneous iotlb
entries") Forbade vhost iotlb msg with null size to prevent entries
with size = start = 0 and last = ULONG_MAX to end up in the iotlb.

Then commit 95932ab2ea07 ("vhost: allow batching hint without size")
only applied the check for VHOST_IOTLB_UPDATE and VHOST_IOTLB_INVALIDATE
message types to fix a regression observed with batching hit.

Still, the introduction of that check introduced a regression for
some users attempting to invalidate the whole ULONG_MAX range by
setting the size to 0. This is the case with qemu/smmuv3/vhost
integration which does not work anymore. It Looks safe to partially
revert the original commit and allow VHOST_IOTLB_INVALIDATE messages
with null size. vhost_iotlb_del_range() will compute a correct end
iova. Same for vhost_vdpa_iotlb_unmap().

Signed-off-by: Eric Auger <eric.auger at redhat.com>
Fixes: e2ae38cf3d91 ("vhost: fix hung thread due to erroneous iotlb
entries")
Cc: stable at vger.kernel.org # v5.17+
Acked-by: Jason Wang <jasowang at redhat.com>

---
v1 -> v2:
- Added Cc stable and Jason's Acked-by
---
 drivers/vhost/vhost.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c71d573f1c94..e0c181ad17e3 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1458,9 +1458,7 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
 		goto done;
 	}
 
-	if ((msg.type == VHOST_IOTLB_UPDATE ||
-	     msg.type == VHOST_IOTLB_INVALIDATE) &&
-	     msg.size == 0) {
+	if (msg.type == VHOST_IOTLB_UPDATE && msg.size == 0) {
 		ret = -EINVAL;
 		goto done;
 	}
-- 
2.41.0

Hi,

On 8/24/23 11:37, Eric Auger wrote:
> Commit e2ae38cf3d91 ("vhost: fix hung thread due to erroneous iotlb
> entries") Forbade vhost iotlb msg with null size to prevent entries
> with size = start = 0 and last = ULONG_MAX to end up in the iotlb.
>
> Then commit 95932ab2ea07 ("vhost: allow batching hint without
size")
> only applied the check for VHOST_IOTLB_UPDATE and VHOST_IOTLB_INVALIDATE
> message types to fix a regression observed with batching hit.
>
> Still, the introduction of that check introduced a regression for
> some users attempting to invalidate the whole ULONG_MAX range by
> setting the size to 0. This is the case with qemu/smmuv3/vhost
> integration which does not work anymore. It Looks safe to partially
> revert the original commit and allow VHOST_IOTLB_INVALIDATE messages
> with null size. vhost_iotlb_del_range() will compute a correct end
> iova. Same for vhost_vdpa_iotlb_unmap().
>
> Signed-off-by: Eric Auger <eric.auger at redhat.com>
> Fixes: e2ae38cf3d91 ("vhost: fix hung thread due to erroneous iotlb
entries")
> Cc: stable at vger.kernel.org # v5.17+
> Acked-by: Jason Wang <jasowang at redhat.com>
Gentle ping for this fix? Any other comments besides Jason's A-b?

Best Regards

Eric
>
> ---
> v1 -> v2:
> - Added Cc stable and Jason's Acked-by
> ---
>  drivers/vhost/vhost.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index c71d573f1c94..e0c181ad17e3 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1458,9 +1458,7 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
>  		goto done;
>  	}
>  
> -	if ((msg.type == VHOST_IOTLB_UPDATE ||
> -	     msg.type == VHOST_IOTLB_INVALIDATE) &&
> -	     msg.size == 0) {
> +	if (msg.type == VHOST_IOTLB_UPDATE && msg.size == 0) {
>  		ret = -EINVAL;
>  		goto done;
>  	}