Re: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Sep 22, 2022 at 08:01:23AM +0000, Eli Cohen wrote:
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Thursday, 22 September 2022 10:53
> > To: Eli Cohen <elic@nvidia.com>
> > Cc: Jason Wang <jasowang@redhat.com>; si-wei.liu@oracle.com; Parav
> > Pandit <parav@nvidia.com>; wuzongyong@linux.alibaba.com;
> > virtualization@lists.linux-foundation.org; linux-kernel@vger.kernel.org;
> > eperezma@redhat.com; lingshan.zhu@intel.com; gdawar@xilinx.com;
> > lulu@redhat.com; xieyongji@bytedance.com
> > Subject: Re: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning
> > 
> > On Thu, Sep 22, 2022 at 07:47:40AM +0000, Eli Cohen wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > Sent: Thursday, 22 September 2022 10:30
> > > > To: Eli Cohen <elic@nvidia.com>
> > > > Cc: Jason Wang <jasowang@redhat.com>; si-wei.liu@oracle.com; Parav
> > > > Pandit <parav@nvidia.com>; wuzongyong@linux.alibaba.com;
> > > > virtualization@lists.linux-foundation.org; linux-kernel@vger.kernel.org;
> > > > eperezma@redhat.com; lingshan.zhu@intel.com; gdawar@xilinx.com;
> > > > lulu@redhat.com; xieyongji@bytedance.com
> > > > Subject: Re: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning
> > > >
> > > > On Thu, Sep 22, 2022 at 05:13:59AM +0000, Eli Cohen wrote:
> > > > > > From: Jason Wang <jasowang@redhat.com>
> > > > > > Sent: Thursday, 22 September 2022 5:43
> > > > > > To: mst@redhat.com; jasowang@redhat.com
> > > > > > Cc: Eli Cohen <elic@nvidia.com>; si-wei.liu@oracle.com; Parav Pandit
> > > > > > <parav@nvidia.com>; wuzongyong@linux.alibaba.com;
> > > > > > virtualization@lists.linux-foundation.org; linux-
> > kernel@vger.kernel.org;
> > > > > > eperezma@redhat.com; lingshan.zhu@intel.com;
> > gdawar@xilinx.com;
> > > > > > lulu@redhat.com; xieyongji@bytedance.com
> > > > > > Subject: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning
> > > > > >
> > > > > > This patch implements features provisioning for vdpa_sim_net.
> > > > > >
> > > > > > 1) validating the provisioned features to be a subset of the parent
> > > > > >    features.
> > > > > > 2) clearing the features that is not wanted by the userspace
> > > > > >
> > > > > > For example:
> > > > > >
> > > > > > # vdpa mgmtdev show
> > > > > > vdpasim_net:
> > > > > >   supported_classes net
> > > > > >   max_supported_vqs 3
> > > > > >   dev_features MTU MAC CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT
> > > > > > VERSION_1 ACCESS_PLATFORM
> > > > > >
> > > > > > 1) provision vDPA device with all features that are supported by the
> > > > > >    net simulator
> > > > > >
> > > > > > # vdpa dev add name dev1 mgmtdev vdpasim_net
> > > > > > # vdpa dev config show
> > > > > > dev1: mac 00:00:00:00:00:00 link up link_announce false mtu 1500
> > > > > >   negotiated_features MTU MAC CTRL_VQ CTRL_MAC_ADDR
> > VERSION_1
> > > > > > ACCESS_PLATFORM
> > > > > >
> > > > > > 2) provision vDPA device with a subset of the features
> > > > > >
> > > > > > # vdpa dev add name dev1 mgmtdev vdpasim_net device_features
> > > > > > 0x300020000
> > > > >
> > > > > How about "features_mask" instead of "device_features"? Could avoid
> > > > confusion.
> > > >
> > > > Not sure I agree.
> > > > features_mask to me would mean it is & with features. Not the case here.
> > > >
> > >
> > >
> > > See the code below
> > >
> > > @@ -254,6 +254,14 @@ static int vdpasim_net_dev_add(struct
> > vdpa_mgmt_dev *mdev, const char *name,
> > >  	dev_attr.work_fn = vdpasim_net_work;
> > >  	dev_attr.buffer_size = PAGE_SIZE;
> > >
> > > +	if (config->mask & BIT_ULL(VDPA_ATTR_DEV_FEATURES)) {
> > > +		if (config->device_features &
> > > +		    ~dev_attr.supported_features)
> > > +			return -EINVAL;
> > > +		dev_attr.supported_features &=
> > > +			 config->device_features;
> > > +	}
> > > +
> > 
> > Oh I didn't notice. It's unnecessary, isn't it?
> > Can just equivalently be
> > 
> > 	dev_attr.supported_features = config->device_features;
> > 
> > right?
> > 
> 
> I don't think so. You want to mask the set of features that the device will offer but you cannot dictate it.

Sure, but it's already a given because device_features is a subset of
supported_features. Observe:

After this line:

         if (config->device_features &
            ~dev_attr.supported_features)
                return -EINVAL;

we know that config->device_features & ~dev_attr.supported_features
is 0.

Therefore logically

config->device_features  == 
    (config->device_features & ~dev_attr.supported_features) |
    (config->device_features & dev_attr.supported_features); 

it follows that

config->device_features  == 
    0 |
    (config->device_features & dev_attr.supported_features); 

and finally

config->device_features  == 
    (config->device_features & dev_attr.supported_features); 


now

		dev_attr.supported_features &=
			 config->device_features;

is equivalent to

		dev_attr.supported_features =
    (config->device_features & dev_attr.supported_features); 

and therefore to

		dev_attr.supported_features = config->device_features;



> > 
> > > > > > # vdpa dev config show
> > > > > > dev1: mac 00:00:00:00:00:00 link up link_announce false mtu 1500
> > > > > >   negotiated_features CTRL_VQ VERSION_1 ACCESS_PLATFORM
> > > > > >
> > > > > > Reviewed-by: Eli Cohen <elic@nvidia.com>
> > > > > > Signed-off-by: Jason Wang <jasowang@redhat.com>
> > > > > > ---
> > > > > >  drivers/vdpa/vdpa_sim/vdpa_sim_net.c | 11 ++++++++++-
> > > > > >  1 file changed, 10 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > > b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > > index 886449e88502..a9ba02be378b 100644
> > > > > > --- a/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > > +++ b/drivers/vdpa/vdpa_sim/vdpa_sim_net.c
> > > > > > @@ -254,6 +254,14 @@ static int vdpasim_net_dev_add(struct
> > > > > > vdpa_mgmt_dev *mdev, const char *name,
> > > > > >  	dev_attr.work_fn = vdpasim_net_work;
> > > > > >  	dev_attr.buffer_size = PAGE_SIZE;
> > > > > >
> > > > > > +	if (config->mask & BIT_ULL(VDPA_ATTR_DEV_FEATURES)) {
> > > > > > +		if (config->device_features &
> > > > > > +		    ~dev_attr.supported_features)
> > > > > > +			return -EINVAL;
> > > > > > +		dev_attr.supported_features &=
> > > > > > +			 config->device_features;
> > > > > > +	}
> > > > > > +
> > > > > >  	simdev = vdpasim_create(&dev_attr);
> > > > > >  	if (IS_ERR(simdev))
> > > > > >  		return PTR_ERR(simdev);
> > > > > > @@ -294,7 +302,8 @@ static struct vdpa_mgmt_dev mgmt_dev = {
> > > > > >  	.id_table = id_table,
> > > > > >  	.ops = &vdpasim_net_mgmtdev_ops,
> > > > > >  	.config_attr_mask = (1 << VDPA_ATTR_DEV_NET_CFG_MACADDR |
> > > > > > -			     1 << VDPA_ATTR_DEV_NET_CFG_MTU),
> > > > > > +			     1 << VDPA_ATTR_DEV_NET_CFG_MTU |
> > > > > > +		             1 << VDPA_ATTR_DEV_FEATURES),
> > > > > >  	.max_supported_vqs = VDPASIM_NET_VQ_NUM,
> > > > > >  	.supported_features = VDPASIM_NET_FEATURES,
> > > > > >  };
> > > > > > --
> > > > > > 2.25.1
> > > > >
> > >
> 

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization