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vhost: Allow null msg.size on VHOST_IOTLB_INVALIDATE

Eric Auger requested to merge eauger1/centos-stream-9:vhost-smmu into main

JIRA: https://issues.redhat.com/browse/RHEL-7126 Upstream Status: v6.6 Tested: On Altra Mount Snow using vSMMU and vhost

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@redhat.com

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