linux-kernel - [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num

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Message-Id: <20190731084655.7024-5-jasowang@redhat.com>
Date:   Wed, 31 Jul 2019 04:46:50 -0400
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, jgg@...pe.ca
Subject: [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr()

The vhost_set_vring_num_addr() could be called in the middle of
invalidate_range_start() and invalidate_range_end(). If we don't reset
invalidate_count after the un-registering of MMU notifier, the
invalidate_cont will run out of sync (e.g never reach zero). This will
in fact disable the fast accessor path. Fixing by reset the count to
zero.

Reported-by: Michael S. Tsirkin <mst@...hat.com>
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/vhost/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2a3154976277..2a7217c33668 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2073,6 +2073,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d,
 		d->has_notifier = false;
 	}
 
+	/* reset invalidate_count in case we are in the middle of
+	 * invalidate_start() and invalidate_end().
+	 */
+	vq->invalidate_count = 0;
 	vhost_uninit_vq_maps(vq);
 #endif
 
-- 
2.18.1