[PATCH v4 5/5] vhost/vsock: add VHOST_RESET_OWNER ioctl
From: Andrey Drobyshev <hidden>
Date: 2026-07-14 15:17:02
Also in:
kvm, lkml, virtualization
Subsystem:
the rest, virtio and vhost vsock driver, virtio host (vhost) · Maintainers:
Linus Torvalds, Stefan Hajnoczi, Stefano Garzarella, "Michael S. Tsirkin", Jason Wang
From: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
This ioctl is needed for QEMU's CPR (checkpoint-restore) migration of
the guest with vhost-vsock device. For this to work, we need to reset
the device ownership on the source side by calling RESET_OWNER, and then
claim it on the dest side by calling SET_OWNER. We expect not to lose any
AF_VSOCK connection while this happens.
To that end, unlike the release path, RESET_OWNER keeps the guest CID
hashed: established connections survive, and host sends issued while
the device is between owners simply stay on send_pkt_queue until the
next device start drains them.
Since the device stays reachable through the CID hash, the lockless
send/cancel paths can race with the worker teardown in
vhost_workers_free(). The previous commit ("vhost: synchronize with
RCU readers when freeing workers") makes that safe.
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrey Drobyshev <redacted>
---
drivers/vhost/vsock.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index d5022d21120b..86f25ff80722 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c@@ -903,6 +903,29 @@ static int vhost_vsock_set_features(struct vhost_vsock *vsock, u64 features) return -EFAULT; } +static long vhost_vsock_reset_owner(struct vhost_vsock *vsock) +{ + struct vhost_iotlb *umem; + long err; + + mutex_lock(&vsock->dev.mutex); + err = vhost_dev_check_owner(&vsock->dev); + if (err) + goto done; + umem = vhost_dev_reset_owner_prepare(); + if (!umem) { + err = -ENOMEM; + goto done; + } + vhost_vsock_drop_backends(vsock); + vhost_vsock_flush(vsock); + vhost_dev_stop(&vsock->dev); + vhost_dev_reset_owner(&vsock->dev, umem); +done: + mutex_unlock(&vsock->dev.mutex); + return err; +} + static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl, unsigned long arg) {
@@ -946,6 +969,8 @@ static long vhost_vsock_dev_ioctl(struct file *f, unsigned int ioctl, return -EOPNOTSUPP; vhost_set_backend_features(&vsock->dev, features); return 0; + case VHOST_RESET_OWNER: + return vhost_vsock_reset_owner(vsock); default: mutex_lock(&vsock->dev.mutex); r = vhost_dev_ioctl(&vsock->dev, ioctl, argp);
--
2.47.1