vhost: mask VIRTIO_F_RING_RESET for vhost and vhost-user devices

Commit 69e1c14aa2 ("virtio: core: vq reset feature negotation support")
enabled VIRTIO_F_RING_RESET by default for all virtio devices.

This feature is not currently emulated by QEMU, so for vhost and
vhost-user devices we need to make sure it is supported by the offloaded
device emulation (in-kernel or in another process).
To do this we need to add VIRTIO_F_RING_RESET to the features bitmap
passed to vhost_get_features(). This way it will be masked if the device
does not support it.

This issue was initially discovered with vhost-vsock and vhost-user-vsock,
and then also tested with vhost-user-rng which confirmed the same issue.
They fail when sending features through VHOST_SET_FEATURES ioctl or
VHOST_USER_SET_FEATURES message, since VIRTIO_F_RING_RESET is negotiated
by the guest (Linux >= v6.0), but not supported by the device.

Fixes: 69e1c14aa2 ("virtio: core: vq reset feature negotation support")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1318
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20221121101101.29400-1-sgarzare@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Acked-by: Jason Wang <jasowang@redhat.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/hw/virtio/vhost-user-rng.c b/hw/virtio/vhost-user-rng.c
index 8b47287875..f9084cde58 100644
--- a/hw/virtio/vhost-user-rng.c
+++ b/hw/virtio/vhost-user-rng.c
@@ -16,6 +16,11 @@
 #include "qemu/error-report.h"
 #include "standard-headers/linux/virtio_ids.h"
 
+static const int feature_bits[] = {
+    VIRTIO_F_RING_RESET,
+    VHOST_INVALID_FEATURE_BIT
+};
+
 static void vu_rng_start(VirtIODevice *vdev)
 {
     VHostUserRNG *rng = VHOST_USER_RNG(vdev);
@@ -106,8 +111,10 @@ static void vu_rng_set_status(VirtIODevice *vdev, uint8_t status)
 static uint64_t vu_rng_get_features(VirtIODevice *vdev,
                                     uint64_t requested_features, Error **errp)
 {
-    /* No feature bits used yet */
-    return requested_features;
+    VHostUserRNG *rng = VHOST_USER_RNG(vdev);
+
+    return vhost_get_features(&rng->vhost_dev, feature_bits,
+                              requested_features);
 }
 
 static void vu_rng_handle_output(VirtIODevice *vdev, VirtQueue *vq)