linux-kernel - [PATCH] vhost: Allow null msg.size on VHOST_IOTLB

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Message-ID: <20230823153032.239304-1-eric.auger@redhat.com>
Date:   Wed, 23 Aug 2023 17:30:32 +0200
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com, elic@...dia.com,
        mail@...rudhrb.com, jasowang@...hat.com, mst@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH] 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@...hat.com>
Fixes: e2ae38cf3d91 ("vhost: fix hung thread due to erroneous iotlb entries")
---
 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