Hi Andrey, thanks for the series! On Fri, Jun 12, 2026 at 07:57:14PM +0300, Andrey Drobyshev wrote:
Host<-->guest connections via AF_VSOCK sockets aren't supposed to outlive VM migration, since VM is moving to another host. However there's a special case, which is QEMU live-update, or CPR (checkpoint-restore) migration. In this case, VM remains on the same host, and we'd like such connections to persist.
In the spec we have VIRTIO_VSOCK_EVENT_TRANSPORT_RESET which is usually sent by the device after a migration.
IIUC the specs don't say this has to be done all the time, so we don't need to change anything in the specs, right?
We just need to avoid sending it (which I think is what we're doing here... I still need to look at the patches).
For this to work, we need to be able to transfer device ownership from source QEMU to dest QEMU. Namely, source needs to reset ownership by issuing VHOST_RESET_OWNER ioctl, and then target has to claim it by calling VHOST_SET_OWNER. Since VHOST_RESET_OWNER isn't yet implemented for vhost-vsock, let's add such implementation (patches 1-2). Also fix regression introduced by the earlier commit [1] (patch 3), and fix the deadlock bug (commit 4).
If it's a regression, should we fix it separately? Or is it related to this series?
There's a complementary series for QEMU [0] adding support of vhost-vsock devices during CPR migration. NOTE: this series needs to be applied on top of Michael's vhost/linux-next tree as it contains relevant commit [1], not yet present in master branch. I've tested this (patched QEMU + patched kernel) approximately as follows: * Run listener in the guest: socat -u VSOCK-LISTEN:9999 - >/tmp/recv.bin * Run data transfer from host to guest: socat -u FILE:/root/bigfile.bin VSOCK-CONNECT:CID:9999 * Perform CPR migration during transfer (either cpr-exec or cpr-transfer) * Check that file hash sum matches [0] https://lore.kernel.org/qemu-devel/[email protected] [1] https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/commit/?id=bb26ed5f3a8b Andrey Drobyshev (1): vhost/vsock: re-scan TX virtqueue on device start Denis V. Lunev (1): vhost/vsock: suppress EHOSTUNREACH fast-fail during CPR pause Pavel Tikhomirov (2): vhost/vsock: split out vhost_vsock_drop_backends helper vhost/vsock: add VHOST_RESET_OWNER ioctl drivers/vhost/vsock.c | 80 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 69 insertions(+), 11 deletions(-) -- 2.47.1
