On Fri, Nov 07, 2025 at 10:01:49AM +0800, Jason Wang wrote:
> We used to clear features silently in virtio_net_get_features() even
> if it is required. This complicates the live migration compatibility
> as the management layer may think the feature is enabled but in fact
> not.
>
> Let's add a strict feature check to make sure if there's a mismatch
> between the required feature and peer, fail the get_features()
> immediately instead of waiting until the migration to fail. This
> offload the migration compatibility completely to the management
> layer.
>
> Signed-off-by: Jason Wang <[email protected]>
Jason, thanks for help looking into the problem!
Am I right that after this patch applied, whenever a new QEMU boots with
the new machine types (e.g. having USO* by default ON), will fail to boot
on an old kernel that doesn't support USO*, but ask the users to turn off
USO* features explicitly in the virtio-net devices?
Thanks,
> ---
> hw/core/machine.c | 1 +
> hw/net/virtio-net.c | 153 +++++++++++++++++++++++++--------
> include/hw/virtio/virtio-net.h | 1 +
> 3 files changed, 119 insertions(+), 36 deletions(-)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 681adbb7ac..a9e43c4990 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -40,6 +40,7 @@
>
> GlobalProperty hw_compat_10_1[] = {
> { TYPE_ACPI_GED, "x-has-hest-addr", "false" },
> + { TYPE_VIRTIO_NET, "strict-peer-feature-check", "false"},
> };
> const size_t hw_compat_10_1_len = G_N_ELEMENTS(hw_compat_10_1);
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 33116712eb..3acc5ed4a6 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -3090,53 +3090,120 @@ static void virtio_net_get_features(VirtIODevice
> *vdev, uint64_t *features,
> virtio_add_feature_ex(features, VIRTIO_NET_F_MAC);
>
> if (!peer_has_vnet_hdr(n)) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_TSO4);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_TSO6);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_ECN);
> -
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_CSUM);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_TSO4);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_TSO6);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_ECN);
> -
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
> -
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
> - virtio_clear_feature_ex(features,
> - VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
> - virtio_clear_feature_ex(features,
> - VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
> + if (n->strict_peer_feature_check) {
> + if (virtio_has_feature_ex(features, VIRTIO_NET_F_CSUM) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_TSO4) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_TSO6) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_ECN) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_CSUM) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_TSO4) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_TSO6) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_ECN) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_USO) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO4) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO6) |
> + virtio_has_feature_ex(features,
> + VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
> + virtio_has_feature_ex(features,
> + VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO) |
> + virtio_has_feature_ex(features,
> +
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM) |
> + virtio_has_feature_ex(features,
> + VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM)
> |
> + virtio_has_feature_ex(features,
> + VIRTIO_NET_F_HASH_REPORT)) {
> + error_setg(errp, "virtio_net: peer doesn't support vnet
> hdr");
> + return;
> + }
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_TSO4);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_TSO6);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_ECN);
> +
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_CSUM);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_TSO4);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_TSO6);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_ECN);
> +
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
> +
> + virtio_clear_feature_ex(features,
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
> + virtio_clear_feature_ex(features,
> VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
> + virtio_clear_feature_ex(features,
> + VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
> + virtio_clear_feature_ex(features,
> + VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
>
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> + }
> }
>
> if (!peer_has_vnet_hdr(n) || !peer_has_ufo(n)) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UFO);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UFO);
> + if (n->strict_peer_feature_check) {
> + if (virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_UFO) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_UFO)) {
> + error_setg(errp, "virtio_net: peer doesn't support UFO");
> + return;
> + }
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UFO);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UFO);
> + }
> }
> if (!peer_has_uso(n)) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
> + if (n->strict_peer_feature_check) {
> + if (virtio_has_feature_ex(features, VIRTIO_NET_F_HOST_USO) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO4) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_GUEST_USO6)) {
> + error_setg(errp, "virtio_net: peer doesn't support USO");
> + return;
> + }
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_USO);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO4);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_USO6);
> + }
> }
>
> if (!peer_has_tunnel(n)) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
> - virtio_clear_feature_ex(features,
> - VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
> - virtio_clear_feature_ex(features,
> - VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
> + if (n->strict_peer_feature_check) {
> + if (virtio_has_feature_ex(features,
> + VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO) |
> + virtio_has_feature_ex(features,
> + VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO) |
> + virtio_has_feature_ex(features,
> +
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM) |
> + virtio_has_feature_ex(features,
> +
> VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM)) {
> + error_setg(errp, "virtio_net: peer doesn't support tunnel
> GSO");
> + return;
> + }
> + } else {
> + virtio_clear_feature_ex(features,
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO);
> + virtio_clear_feature_ex(features,
> VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO);
> + virtio_clear_feature_ex(features,
> + VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM);
> + virtio_clear_feature_ex(features,
> + VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO_CSUM);
> + }
> }
>
> if (!get_vhost_net(nc->peer)) {
> if (!use_own_hash) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_RSS);
> + if (n->strict_peer_feature_check) {
> + if (virtio_has_feature_ex(features,
> VIRTIO_NET_F_HASH_REPORT) |
> + virtio_has_feature_ex(features, VIRTIO_NET_F_RSS)) {
> + error_setg(errp,
> + "virtio_net: peer doesn't support
> RSS/HASH_REPORT");
> + return;
> + }
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_RSS);
> + }
> } else if (virtio_has_feature_ex(features, VIRTIO_NET_F_RSS)) {
> virtio_net_load_ebpf(n, errp);
> }
> @@ -3145,14 +3212,26 @@ static void virtio_net_get_features(VirtIODevice
> *vdev, uint64_t *features,
> }
>
> if (!use_peer_hash) {
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> + if (n->strict_peer_feature_check &&
> + virtio_has_feature_ex(features, VIRTIO_NET_F_HASH_REPORT)) {
> + error_setg(errp, "virtio_net: peer doesn't HASH_REPORT");
> + return;
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_HASH_REPORT);
> + }
>
> if (!use_own_hash || !virtio_net_attach_ebpf_to_backend(n->nic, -1))
> {
> if (!virtio_net_load_ebpf(n, errp)) {
> return;
> }
>
> - virtio_clear_feature_ex(features, VIRTIO_NET_F_RSS);
> + if (n->strict_peer_feature_check &&
> + virtio_has_feature_ex(features, VIRTIO_NET_F_RSS)) {
> + error_setg(errp, "virtio_net: fail to attach eBPF for RSS");
> + return;
> + } else {
> + virtio_clear_feature_ex(features, VIRTIO_NET_F_RSS);
> + }
> }
> }
>
> @@ -4313,6 +4392,8 @@ static const Property virtio_net_properties[] = {
> host_features_ex,
> VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO_CSUM,
> false),
> + DEFINE_PROP_BOOL("strict-peer-feature-check", VirtIONet,
> + strict_peer_feature_check, true),
> };
>
> static void virtio_net_class_init(ObjectClass *klass, const void *data)
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 5b8ab7bda7..abd4ca4bb0 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -222,6 +222,7 @@ struct VirtIONet {
> /* primary failover device is hidden*/
> bool failover_primary_hidden;
> bool failover;
> + bool strict_peer_feature_check;
> DeviceListener primary_listener;
> QDict *primary_opts;
> bool primary_opts_from_json;
> --
> 2.34.1
>
--
Peter Xu
