qemu-kvm/kvm-vhost-backend-implement-extended-features-support.patch

From d0e31af77cd51df8c17fa4d304571f8b1eb5ce29 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <pabeni@redhat.com>
Date: Mon, 22 Sep 2025 16:18:24 +0200
Subject: [PATCH 15/19] vhost-backend: implement extended features support

RH-Author: Laurent Vivier <lvivier@redhat.com>
RH-MergeRequest: 456: backport support for GSO over UDP tunnel offload
RH-Jira: RHEL-143785
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: MST <mst@redhat.com>
RH-Commit: [10/14] bd12c2f08dad502a7359d4344a2220b10ac96a48 (lvivier/qemu-kvm-centos)

JIRA: https://issues.redhat.com/browse/RHEL-143785

Leverage the kernel extended features manipulation ioctls(), if
available, and fallback to old ops otherwise. Error out when setting
extended features but kernel support is not available.

Note that extended support for get/set backend features is not needed,
as the only feature that can be changed belongs to the 64 bit range.

Reviewed-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <150daade3d59e77629276920e014ee8e5fc12121.1758549625.git.pabeni@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit f412c1f57ab58fd595efee26264193759220ca6f)
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/virtio/vhost-backend.c | 62 ++++++++++++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 11 deletions(-)

diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index 833804dd40..4367db0d95 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -20,6 +20,11 @@
 #include <linux/vhost.h>
 #include <sys/ioctl.h>
 
+struct vhost_features {
+    uint64_t count;
+    uint64_t features[VIRTIO_FEATURES_NU64S];
+};
+
 static int vhost_kernel_call(struct vhost_dev *dev, unsigned long int request,
                              void *arg)
 {
@@ -182,12 +187,6 @@ static int vhost_kernel_get_vring_worker(struct vhost_dev *dev,
     return vhost_kernel_call(dev, VHOST_GET_VRING_WORKER, worker);
 }
 
-static int vhost_kernel_set_features(struct vhost_dev *dev,
-                                     uint64_t features)
-{
-    return vhost_kernel_call(dev, VHOST_SET_FEATURES, &features);
-}
-
 static int vhost_kernel_set_backend_cap(struct vhost_dev *dev)
 {
     uint64_t features;
@@ -210,10 +209,51 @@ static int vhost_kernel_set_backend_cap(struct vhost_dev *dev)
     return 0;
 }
 
-static int vhost_kernel_get_features(struct vhost_dev *dev,
-                                     uint64_t *features)
+static int vhost_kernel_set_features(struct vhost_dev *dev,
+                                     const uint64_t *features)
 {
-    return vhost_kernel_call(dev, VHOST_GET_FEATURES, features);
+    struct vhost_features farray;
+    bool extended_in_use;
+    int r;
+
+    farray.count = VIRTIO_FEATURES_NU64S;
+    virtio_features_copy(farray.features, features);
+    extended_in_use = virtio_features_use_ex(farray.features);
+
+    /*
+     * Can't check for ENOTTY: for unknown ioctls the kernel interprets
+     * the argument as a virtio queue id and most likely errors out validating
+     * such id, instead of reporting an unknown operation.
+     */
+    r = vhost_kernel_call(dev, VHOST_SET_FEATURES_ARRAY, &farray);
+    if (!r) {
+        return 0;
+    }
+
+    if (extended_in_use) {
+        error_report("Trying to set extended features without kernel support");
+        return -EINVAL;
+    }
+    return vhost_kernel_call(dev, VHOST_SET_FEATURES, &farray.features[0]);
+}
+
+static int vhost_kernel_get_features(struct vhost_dev *dev, uint64_t *features)
+{
+    struct vhost_features farray;
+    int r;
+
+    farray.count = VIRTIO_FEATURES_NU64S;
+    r = vhost_kernel_call(dev, VHOST_GET_FEATURES_ARRAY, &farray);
+    if (r) {
+        memset(&farray, 0, sizeof(farray));
+        r = vhost_kernel_call(dev, VHOST_GET_FEATURES, &farray.features[0]);
+    }
+    if (r) {
+        return r;
+    }
+
+    virtio_features_copy(features, farray.features);
+    return 0;
 }
 
 static int vhost_kernel_set_owner(struct vhost_dev *dev)
@@ -341,8 +381,8 @@ const VhostOps kernel_ops = {
         .vhost_attach_vring_worker = vhost_kernel_attach_vring_worker,
         .vhost_new_worker = vhost_kernel_new_worker,
         .vhost_free_worker = vhost_kernel_free_worker,
-        .vhost_set_features = vhost_kernel_set_features,
-        .vhost_get_features = vhost_kernel_get_features,
+        .vhost_set_features_ex = vhost_kernel_set_features,
+        .vhost_get_features_ex = vhost_kernel_get_features,
         .vhost_set_backend_cap = vhost_kernel_set_backend_cap,
         .vhost_set_owner = vhost_kernel_set_owner,
         .vhost_get_vq_index = vhost_kernel_get_vq_index,
-- 
2.47.3