[PATCH] vhost-vsock: fix migration issue when seqpacket is supported

[Stefano Garzarella <sgarzare@redhat.com>]

Commit 1e08fd0a46 ("vhost-vsock: SOCK_SEQPACKET feature bit support")
enabled the SEQPACKET feature bit.
This commit is released with QEMU 6.1, so if we try to migrate a VM where
the host kernel supports SEQPACKET but machine type version is less than
6.1, we get the following errors:

    Features 0x130000002 unsupported. Allowed features: 0x179000000
    Failed to load virtio-vhost_vsock:virtio
    error while loading state for instance 0x0 of device '0000:00:05.0/virtio-vhost_vsock'
    load of migration failed: Operation not permitted

Let's disable the feature bit for machine types < 6.1, adding a
`features` field to VHostVSock to simplify the handling of upcoming
features we will support.

Fixes: 1e08fd0a46 ("vhost-vsock: SOCK_SEQPACKET feature bit support")
Cc: qemu-stable@nongnu.org
Reported-by: Jiang Wang <jiang.wang@bytedance.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 include/hw/virtio/vhost-vsock.h | 1 +
 hw/core/machine.c               | 1 +
 hw/virtio/vhost-vsock.c         | 6 +++++-
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/hw/virtio/vhost-vsock.h b/include/hw/virtio/vhost-vsock.h
index 84f4e727c7..7da92a8883 100644
--- a/include/hw/virtio/vhost-vsock.h
+++ b/include/hw/virtio/vhost-vsock.h
@@ -29,6 +29,7 @@ struct VHostVSock {
     /*< private >*/
     VHostVSockCommon parent;
     VHostVSockConf conf;
+    uint64_t features;
 
     /*< public >*/
 };
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 067f42b528..7e2851feb9 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -46,6 +46,7 @@ GlobalProperty hw_compat_6_0[] = {
     { "nvme-ns", "eui64-default", "off"},
     { "e1000", "init-vet", "off" },
     { "e1000e", "init-vet", "off" },
+    { "vhost-vsock-device", "seqpacket", "off" },
 };
 const size_t hw_compat_6_0_len = G_N_ELEMENTS(hw_compat_6_0);
 
diff --git a/hw/virtio/vhost-vsock.c b/hw/virtio/vhost-vsock.c
index 1b1a5c70ed..9458d4eeb4 100644
--- a/hw/virtio/vhost-vsock.c
+++ b/hw/virtio/vhost-vsock.c
@@ -114,8 +114,10 @@ static uint64_t vhost_vsock_get_features(VirtIODevice *vdev,
                                          Error **errp)
 {
     VHostVSockCommon *vvc = VHOST_VSOCK_COMMON(vdev);
+    VHostVSock *vsock = VHOST_VSOCK(vdev);
+
+    requested_features |= vsock->features;
 
-    virtio_add_feature(&requested_features, VIRTIO_VSOCK_F_SEQPACKET);
     return vhost_get_features(&vvc->vhost_dev, feature_bits,
                                 requested_features);
 }
@@ -218,6 +220,8 @@ static void vhost_vsock_device_unrealize(DeviceState *dev)
 static Property vhost_vsock_properties[] = {
     DEFINE_PROP_UINT64("guest-cid", VHostVSock, conf.guest_cid, 0),
     DEFINE_PROP_STRING("vhostfd", VHostVSock, conf.vhostfd),
+    DEFINE_PROP_BIT64("seqpacket", VHostVSock, features,
+                      VIRTIO_VSOCK_F_SEQPACKET, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
-- 
2.31.1