On 19.06.2026 12:55, Andrey Drobyshev wrote:
When preserving a vhost fd using CPR, call VHOST_RESET_OWNER prior to CPR
in old QEMU. Otherwise, new QEMU will fail when it calls VHOST_SET_OWNER
during vhost_dev_init.
This patch is a rework of the change originally proposed by Steve, Ben
and Mark at [0].
[0]
https://lore.kernel.org/qemu-devel/[email protected]
Originally-by: Mark Kanda <[email protected]>
Originally-by: Steve Sistare <[email protected]>
Originally-by: Ben Chaney <[email protected]>
Signed-off-by: Andrey Drobyshev <[email protected]>
---
hw/virtio/vhost-kernel.c | 6 ++++++
hw/virtio/vhost.c | 33 +++++++++++++++++++++++++++++++
include/hw/virtio/vhost-backend.h | 1 +
include/hw/virtio/vhost.h | 1 +
4 files changed, 41 insertions(+)
diff --git a/hw/virtio/vhost-kernel.c b/hw/virtio/vhost-kernel.c
index 3390b48c6f1..55d316b88e9 100644
--- a/hw/virtio/vhost-kernel.c
+++ b/hw/virtio/vhost-kernel.c
@@ -261,6 +261,11 @@ static int vhost_kernel_set_owner(struct vhost_dev *dev)
return vhost_kernel_call(dev, VHOST_SET_OWNER, NULL);
}
+static int vhost_kernel_reset_owner(struct vhost_dev *dev)
+{
+ return vhost_kernel_call(dev, VHOST_RESET_OWNER, NULL);
+}
+
static int vhost_kernel_get_vq_index(struct vhost_dev *dev, int idx)
{
assert(idx >= dev->vq_index && idx < dev->vq_index + dev->nvqs);
@@ -385,6 +390,7 @@ const VhostOps kernel_ops = {
.vhost_get_features_ex = vhost_kernel_get_features,
.vhost_set_backend_cap = vhost_kernel_set_backend_cap,
.vhost_set_owner = vhost_kernel_set_owner,
+ .vhost_reset_owner = vhost_kernel_reset_owner,
.vhost_get_vq_index = vhost_kernel_get_vq_index,
.vhost_vsock_set_guest_cid = vhost_kernel_vsock_set_guest_cid,
.vhost_vsock_set_running = vhost_kernel_vsock_set_running,
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index af41841b529..1521b50cbff 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -24,6 +24,7 @@
#include "standard-headers/linux/vhost_types.h"
#include "hw/virtio/virtio-bus.h"
#include "hw/mem/memory-device.h"
+#include "migration/misc.h"
#include "migration/blocker.h"
#include "migration/qemu-file-types.h"
#include "system/dma.h"
@@ -1667,6 +1668,32 @@ static int vhost_dev_init_features(struct vhost_dev
*hdev)
return r;
}
+static int vhost_cpr_notifier(NotifierWithReturn *notifier,
+ MigrationEvent *e, Error **errp)
+{
+ struct vhost_dev *dev;
+ int r;
+
+ dev = container_of(notifier, struct vhost_dev, cpr_notifier);
+
+ if (dev->vhost_ops->backend_type != VHOST_BACKEND_TYPE_KERNEL) {
+ return 0;
+ }
+
+ if (e->type == MIG_EVENT_SETUP) {
+ r = dev->vhost_ops->vhost_reset_owner(dev);
+ if (r < 0) {
+ VHOST_OPS_DEBUG(r, "vhost_reset_owner failed");
Shouldn't we abort the migration attempt here?
+ }
+ } else if (e->type == MIG_EVENT_FAILED) {
+ r = dev->vhost_ops->vhost_set_owner(dev);
+ if (r < 0) {
+ VHOST_OPS_DEBUG(r, "vhost_set_owner failed");
What would be the impact on the guest of this failure?
Shouldn't we *at least* unconditionally print error here?
Maybe even more if guest would be unsafe in this condition?
+ }
+ }
+ return 0;
+}
+
Thanks,
Maciej
