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

[Jason Wang <jasowang@redhat.com>]

在 2021/6/4 下午5:10, Gautam Dawar 写道:
> Hi Jason,
>
> -----Original Message-----
> From: Jason Wang <jasowang@redhat.com>
> Sent: Wednesday, June 2, 2021 2:18 PM
> To: Gautam Dawar <gdawar@xilinx.com>; mst@redhat.com; qemu-devel@nongnu.org
> Cc: lulu@redhat.com; qemu-stable@nongnu.org
> Subject: Re: [PATCH 1/2] vhost-vdpa: don't initialize backend_features
>
> Hi Gautam:
>
> 在 2021/6/2 下午3:38, Gautam Dawar 写道:
>> 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.
>
> See vhost_net_init:
>
>       struct vhost_net *net = g_new0(struct vhost_net, 1);
>
> vhost_dev is embedded in the vhost_net structure. So I think it should be zero.
>
> [GD>>]  That's correct. The embedded vhost_dev structure is indeed getting cleared to 0 in vhost_net_init().
> Thanks


Ok, I've queued this patch.

Thanks


>
>
>>        v->listener = vhost_vdpa_memory_listener;
>>        v->msg_type = VHOST_IOTLB_MSG_V2;
>>    
>> --
>> 2.25.1
>>
> [GD>>]
> Signed-off-by: Gautam Dawar <gdawar@xilinx.com>
> Acked-by: Gautam Dawar <gdawar@xilinx.com>
>