RE: [PATCH 1/2] vhost-vdpa: don't initialize backend_features

[Gautam Dawar]

Hi Jason,

Pls see my comments inline marked by GD>>

Regards,
Gautam

-----Original Message-----
From: Jason Wang <jasowang@redhat.com> 
Sent: Wednesday, June 2, 2021 9:01 AM
To: mst@redhat.com; qemu-devel@nongnu.org
Cc: Gautam Dawar <gdawar@xilinx.com>; lulu@redhat.com; Jason Wang 
<jasowang@redhat.com>; qemu-stable@nongnu.org
Subject: [PATCH 1/2] vhost-vdpa: don't initialize backend_features

We used to initialize backend_features during vhost_vdpa_init() regardless 
whether or not it was supported by vhost. This will lead the unsupported 
features like VIRTIO_F_IN_ORDER to be included and set to the vhost-vdpa during 
vhost_dev_start. Because the VIRTIO_F_IN_ORDER is not supported by vhost-vdpa 
so it won't be advertised to guest which will break the datapath.

Fix this by not initializing the backend_features, so the acked_features could 
be built only from guest features via vhost_net_ack_features().

Fixes: 108a64818e69b ("vhost-vdpa: introduce vhost-vdpa backend")
Cc: qemu-stable@nongnu.org
Cc: Gautam Dawar <gdawar@xilinx.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/virtio/vhost-vdpa.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c index 
01d2101d09..5fe43a4eb5 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -275,15 +275,12 @@ static void vhost_vdpa_add_status(struct vhost_dev *dev, 
uint8_t status)  static int vhost_vdpa_init(struct vhost_dev *dev, void 
*opaque)  {
     struct vhost_vdpa *v;
-    uint64_t features;
     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA);
     trace_vhost_vdpa_init(dev, opaque);
 
     v = opaque;
     v->dev = dev;
     dev->opaque =  opaque ;
-    vhost_vdpa_call(dev, VHOST_GET_FEATURES, &features);
-    dev->backend_features = features;
[GD>>] Should this be initialized with 0 here? I am not sure if  memory 
allocated for struct vhost_dev is initialized with 0.
     v->listener = vhost_vdpa_memory_listener;
     v->msg_type = VHOST_IOTLB_MSG_V2;
 
--
2.25.1