On 2026/09/30 2:23, Andrey Drobyshev wrote:
The previous patches reuse the source vhost FD on the destination,
however both source and target still call vhost_dev_init() (VHOST_SET_OWNER)
in realize(). For cpr-transfer the destination realizes while the source
still owns the shared FD, so its SET_OWNER would fail - ownership has to be
handed over explicitly.
Do this through the device's CPR vmstate hooks. Namely, release device
ownership in pre_save, reclaim in post_load, re-acquire on restart:
- .pre_save() releases ownership on the source (VHOST_RESET_OWNER) once
the VM is stopped, for the FD-preserving CPR modes (cpr-transfer and
cpr-exec).
- .realize(), for an incoming CPR, only sets up the virtio device and
queries the backend features by calling vhost_dev_init_backend().
It doesn't take device ownership and doesn't touch the VQs which
still-running source might use. The full init is deferred to
.post_load().
- .post_load() reclaims it on the destination: the full vhost_dev_init()
(VHOST_SET_OWNER) on the preserved FD, plus sets the guest cid, before
the device is started at vm_start.
- .set_status() refuses to start a device whose init hasn't completed
yet (incoming CPR before post_load).
- .set_status() re-acquires ownership before starting the device if
pre_save released it and this QEMU is about to run the guest again:
the migration failed, or it completed and the management resumed the
source (e.g. cpr-transfer target died).
With the handoff in place, lift the CPR blocker.
Note: this requires kernel side support of VHOST_RESET_OWNER operation
for vhost-vsock. Otherwise CPR attempt fails in .pre_save().
Suggested-by: Dongli Zhang <[email protected]>
Reviewed-by: Stefano Garzarella <[email protected]>
Signed-off-by: Andrey Drobyshev <[email protected]>
---
hw/virtio/vhost-vsock.c | 157 ++++++++++++++++++++++++++++++++--------
include/hw/virtio/vhost-vsock.h | 2 +-
2 files changed, 128 insertions(+), 31 deletions(-)
diff --git a/hw/virtio/vhost-vsock.c b/hw/virtio/vhost-vsock.c
index 6e89007b2ce..65ba573da4d 100644
--- a/hw/virtio/vhost-vsock.c
+++ b/hw/virtio/vhost-vsock.c
@@ -21,7 +21,6 @@
#include "hw/virtio/vhost-vsock.h"
#include "monitor/monitor.h"
#include "migration/cpr.h"
-#include "migration/blocker.h"
#include "migration/misc.h"
static void vhost_vsock_get_config(VirtIODevice *vdev, uint8_t *config)
@@ -85,14 +84,46 @@ static char *vhost_vsock_cpr_name(DeviceState *dev)
static int vhost_vsock_set_status(VirtIODevice *vdev, uint8_t status)
{
VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(vdev);
+ VHostVSock *vsock = VHOST_VSOCK(vdev);
bool should_start = virtio_device_should_start(vdev, status);
int ret;
+ /*
+ * During CPR, on target the full vhost_dev_init() is deferred to
+ * post_load. Refuse to start a half-initialised device rather than
+ * issue vhost ioctls on it.
+ */
+ if (should_start && !vhost_dev_is_initialized(&vvc->vhost_dev)) {
+ error_report("vhost-vsock: refusing to start, device init incomplete");
+ return 0;
+ }
+
if (vhost_dev_is_started(&vvc->vhost_dev) == should_start) {
return 0;
}
if (should_start) {
+ /*
+ * vsock->owner_reset is only set in .pre_save() on CPR migration
+ * source, after a successful RESET_OWNER op. If we end up here
+ * with this flag set - that means that either CPR migration failed,
+ * or we got 'cont' cmd from the management (e.g. cpr-transfer
+ * target died). In either case, we need to re-acquire device
+ * ownership.
+ *
+ * On failure leave the device stopped. The next start attempt
+ * (guest driver reset, VM stop/cont) retries.
+ */
+ if (vsock->owner_reset) {
+ ret = vhost_dev_set_owner(&vvc->vhost_dev);
+ if (ret < 0) {
+ error_report("vhost-vsock: cannot re-acquire device "
+ "ownership: %s", strerror(-ret));
+ return 0;
+ }
+ vsock->owner_reset = false;
+ }
+
ret = vhost_vsock_common_start(vdev);
if (ret < 0) {
return 0;
@@ -123,8 +154,44 @@ static uint64_t vhost_vsock_get_features(VirtIODevice
*vdev,
return vhost_vsock_common_get_features(vdev, requested_features, errp);
}
+static int vhost_vsock_pre_save(void *opaque)
+{
+ VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(opaque);
+ VHostVSock *vsock = VHOST_VSOCK(opaque);
+ int ret;
+
+ ret = vhost_vsock_common_pre_save(opaque);
+ if (ret) {
+ return ret;
+ }
+
+ /*
+ * Release the device ownership now for CPR migration. The device is
+ * already stopped at pre_save, and destination reclaims it by calling
+ * VHOST_SET_OWNER in post_load.
+ */
+ if (cpr_incoming_needed(NULL) && migration_is_running() &&
+ !vsock->owner_reset) {
+ ret = vhost_dev_reset_owner(&vvc->vhost_dev);
+ if (ret < 0) {
+ error_report("vhost-vsock: vhost_reset_owner failed: %s",
+ strerror(-ret));
+ return ret;
+ }
+ vsock->owner_reset = true;
+ }
+
+ return 0;
+}
+
static int vhost_vsock_post_load(void *opaque, int version_id)
{
+ VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(opaque);
+ VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
+ g_autofree char *cpr_name = vhost_vsock_cpr_name(DEVICE(opaque));
+ Error *local_err = NULL;
+ int vhostfd, ret;
+
/*
* Only reset vsock connections for non-CPR migration. For CPR the
* guest cid is unchanged, and the cid-change reset would otherwise
@@ -134,6 +201,35 @@ static int vhost_vsock_post_load(void *opaque, int
version_id)
return vhost_vsock_common_post_load(opaque, version_id);
}
+ /*
+ * CPR restore case. The source released device ownership in its
+ * pre_save. Complete the handoff here, before the device is started
+ * at vm_start. Init vhost device on preserved FD, issue
+ * VHOST_SET_OWNER on it, and restore the guest cid.
+ */
+ vhostfd = cpr_find_fd(cpr_name, 0);
+ if (vhostfd < 0) {
+ error_report("vhost-vsock: could not find restored vhost FD");
+ return -1;
+ }
+
+ ret = vhost_dev_init(&vvc->vhost_dev, (void *)(uintptr_t)vhostfd,
vhost_dev_init() can successfully issue SET_OWNER and then fail during
virtqueue initialization or memory-slot validation. Its cleanup only
closes the destination FD; the source still holds the same underlying
file, so the kernel retains the destination owner. Resuming the source
then makes vhost_vsock_set_status() repeatedly fail SET_OWNER with
EBUSY, leaving vsock unusable.
I also suggest using GINT_TO_POINTER().
Regards,
Akihiko Odaki
+ VHOST_BACKEND_TYPE_KERNEL, 0, &local_err);
+ if (ret < 0) {
+ error_report_err(local_err);
+ cpr_delete_fd(cpr_name, 0);
+ return ret;
+ }
+
+ ret = vhost_vsock_set_guest_cid(vdev);
+ if (ret < 0) {
+ error_report("vhost-vsock: unable to set guest cid: %s",
+ strerror(-ret));
+ vhost_dev_cleanup(&vvc->vhost_dev);
+ cpr_delete_fd(cpr_name, 0);
+ return ret;
+ }
+
return 0;
}
@@ -145,7 +241,7 @@ static const VMStateDescription vmstate_virtio_vhost_vsock = {
VMSTATE_VIRTIO_DEVICE,
VMSTATE_END_OF_LIST()
},
- .pre_save = vhost_vsock_common_pre_save,
+ .pre_save = vhost_vsock_pre_save,
.post_load = vhost_vsock_post_load,
};
@@ -171,37 +267,24 @@ static void vhost_vsock_device_realize(DeviceState *dev, Error **errp)
return;
}
- /*
- * CPR migration of a vhost-vsock device is not supported yet: the
- * device ownership is not handed over, so the target fails to set
- * up its device. Fail the migration early and gracefully instead.
- */
- error_setg(&vsock->migration_blocker,
- "vhost-vsock: CPR migration is not supported");
- if (migrate_add_blocker_modes(&vsock->migration_blocker,
- BIT(MIG_MODE_CPR_TRANSFER) |
- BIT(MIG_MODE_CPR_EXEC), errp) < 0) {
- return;
- }
-
if (cpr_incoming) {
/* Reuse the fd handed over from the source QEMU */
vhostfd = cpr_find_fd(cpr_name, 0);
if (vhostfd < 0) {
error_setg(errp, "vhost-vsock: could not find restored vhost FD");
- goto err_blocker;
+ return;
}
} else if (vsock->conf.vhostfd) {
vhostfd = monitor_fd_param(monitor_cur(), vsock->conf.vhostfd, errp);
if (vhostfd == -1) {
error_prepend(errp, "vhost-vsock: unable to parse vhostfd: ");
- goto err_blocker;
+ return;
}
} else {
vhostfd = open("/dev/vhost-vsock", O_RDWR);
if (vhostfd < 0) {
error_setg_file_open(errp, errno, "/dev/vhost-vsock");
- goto err_blocker;
+ return;
}
}
@@ -210,19 +293,37 @@ static void vhost_vsock_device_realize(DeviceState *dev, Error **errp)
if (cpr_incoming) {
cpr_delete_fd(cpr_name, 0);
}
- goto err_blocker;
+ return;
}
vhost_vsock_common_realize(vdev);
- ret = vhost_dev_init(&vvc->vhost_dev, (void *)(uintptr_t)vhostfd,
- VHOST_BACKEND_TYPE_KERNEL, 0, errp);
- if (ret < 0) {
+ if (!cpr_incoming) {
+ ret = vhost_dev_init(&vvc->vhost_dev, (void *)(uintptr_t)vhostfd,
+ VHOST_BACKEND_TYPE_KERNEL, 0, errp);
+ if (ret < 0) {
+ /*
+ * vhostfd is closed by vhost_dev_cleanup, which is called
+ * by vhost_dev_init on initialization error.
+ */
+ goto err_virtio;
+ }
+ } else {
/*
- * vhostfd is closed by vhost_dev_cleanup, which is called
- * by vhost_dev_init on initialization error.
+ * CPR restore case: only learn the backend feature set now, but
+ * defer taking ownership or touching VQs (the still-running source
+ * might be using them). The full vhost_dev_init()/VHOST_SET_OWNER
+ * is done later in post_load.
*/
- goto err_virtio;
+ ret = vhost_dev_init_backend(&vvc->vhost_dev,
+ (void *)(uintptr_t)vhostfd,
+ VHOST_BACKEND_TYPE_KERNEL, errp);
+ if (ret < 0) {
+ /* vhost_dev_init_backend() does not close the fd on error */
+ goto err_vhost_dev;
+ }
+
+ return;
}
ret = vhost_vsock_set_guest_cid(vdev);
@@ -232,7 +333,7 @@ static void vhost_vsock_device_realize(DeviceState *dev,
Error **errp)
}
/* Register the fd for a future CPR after a fully successful realize */
- if (!cpr_incoming && !cpr_save_fd(cpr_name, 0, vhostfd, errp)) {
+ if (!cpr_save_fd(cpr_name, 0, vhostfd, errp)) {
goto err_vhost_dev;
}
@@ -247,22 +348,18 @@ err_vhost_dev:
}
err_virtio:
vhost_vsock_common_unrealize(vdev);
-err_blocker:
- migrate_del_blocker(&vsock->migration_blocker);
}
static void vhost_vsock_device_unrealize(DeviceState *dev)
{
VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(dev);
VirtIODevice *vdev = VIRTIO_DEVICE(dev);
- VHostVSock *vsock = VHOST_VSOCK(dev);
g_autofree char *cpr_name = vhost_vsock_cpr_name(dev);
/* This will stop vhost backend if appropriate. */
vhost_vsock_set_status(vdev, 0);
cpr_delete_fd(cpr_name, 0);
- migrate_del_blocker(&vsock->migration_blocker);
vhost_dev_cleanup(&vvc->vhost_dev);
vhost_vsock_common_unrealize(vdev);
}
diff --git a/include/hw/virtio/vhost-vsock.h b/include/hw/virtio/vhost-vsock.h
index a964d57e1bc..6e1c39383ef 100644
--- a/include/hw/virtio/vhost-vsock.h
+++ b/include/hw/virtio/vhost-vsock.h
@@ -29,7 +29,7 @@ struct VHostVSock {
/*< private >*/
VHostVSockCommon parent;
VHostVSockConf conf;
- Error *migration_blocker; /* CPR migration is not supported */
+ bool owner_reset; /* CPR released ownership; needs re-acquire */
/*< public >*/
};
