On Wed, Nov 12, 2025 at 04:55:42PM -0500, Peter Xu wrote:
> 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?
What kernel version are we talking about where there will be
incompatibility ? Is it old enough that it pre-dates our
platform support matrix requirements ? Ubuntu 22.04 and
RHEL-9 are currently our targets with the oldest kernels
that we need to retain compatibility with as the bare min.
I would expect machine types to work on these old platforms
without users to having to manually disable default set
features.
>
> 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
>
With regards,
Daniel
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