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

[Stefano Garzarella]

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

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>