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[PATCH 34/40] vdpa: fix network breakage after cancelling migration


From: Si-Wei Liu
Subject: [PATCH 34/40] vdpa: fix network breakage after cancelling migration
Date: Thu, 7 Dec 2023 09:39:47 -0800

Fix an issue where cancellation of ongoing migration ends up
with no network connectivity.

When canceling migration, SVQ will be switched back to the
passthrough mode, but the right call fd is not programed to
the device and the svq's own call fd is still used. At the
point of this transitioning period, the shadow_vqs_enabled
hadn't been set back to false yet, causing the installation
of call fd inadvertently bypassed.

Fixes: a8ac88585da1 ("vhost: Add Shadow VirtQueue call forwarding capabilities")
Cc: Eugenio PĂ©rez <eperezma@redhat.com>

Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
---
 hw/virtio/vhost-vdpa.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 4010fd9..8ba390d 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1647,7 +1647,12 @@ static int vhost_vdpa_set_vring_call(struct vhost_dev 
*dev,
 
     /* Remember last call fd because we can switch to SVQ anytime. */
     vhost_svq_set_svq_call_fd(svq, file->fd);
-    if (v->shadow_vqs_enabled) {
+    /*
+     * In the event of SVQ switching to off, shadow_vqs_enabled has
+     * not been set to false yet, but the underlying call fd will
+     * switch back to the guest notifier for passthrough VQs.
+     */
+    if (v->shadow_vqs_enabled && v->shared->svq_switching >= 0) {
         return 0;
     }
 
-- 
1.8.3.1




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