On Mon, Jul 20, 2026 at 01:22:38PM +0300, Andrey Drobyshev wrote:
Earlier commit bb26ed5f3a8b ("vhost/vsock: Refuse the connection immediately when guest isn't ready") added a fast-fail in vhost_transport_send_pkt(). It rejects every host send with -EHOSTUNREACH until the destination calls SET_RUNNING(1). The fast-fail condition checks whether device's backends are dropped, and if they're, the guest is considered to be not ready.However, there might be other reasons for backends to be nulled. In particular, when QEMU is performing CPR (checkpoint-restore) migration, device ownership is being RESET and SET again, which leads to backends drop and reattach. If we end up connecting during this window, an AF_VSOCK client gets -EHOSTUNREACH, which is wrong. Add an 'ever_started' flag which is set once in vhost_vsock_start() and is never cleared. The behaviour changes to: * When device was never started -> flag is unset -> no listener can exist yet -> fast-fail; * Once the device starts -> flag is set -> we don't fast-fail -> we queue and preserve during any later stop / CPR pause. The VHOST_RESET_OWNER ioctl is implemented in a following patch, and without RESET_OWNER the problem we fix here isn't manifesting - thus this patch is a preparation to support RESET_OWNER. Important caveat: after the first start, a connect during any stopped window is queued instead of fast-failed. That was the behaviour before the patch bb26ed5f3a8b, and we're restoring it now. However we still keep the behaviour originally intended by that commit (i.e. fast-fail if there's no real listener yet) while fixing the CPR path. Suggested-by: Stefano Garzarella <[email protected]> Signed-off-by: Denis V. Lunev <[email protected]> Signed-off-by: Andrey Drobyshev <[email protected]> Reviewed-by: Pavel Tikhomirov <[email protected]> --- drivers/vhost/vsock.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
Reviewed-by: Stefano Garzarella <[email protected]>
