Re: [PATCH v5 5/5] vhost/vsock: add VHOST_RESET_OWNER ioctl

On Mon, Jul 20, 2026 at 01:22:41PM +0300, Andrey Drobyshev wrote:
>From: Pavel Tikhomirov <[email protected]>
>
>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 <[email protected]>
>Signed-off-by: Andrey Drobyshev <[email protected]>
>---
> drivers/vhost/vsock.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)

Reviewed-by: Stefano Garzarella <[email protected]>