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

From: Michael S. Tsirkin
Date: Thu Sep 22 2022 - 05:12:21 EST

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On Thu, Sep 22, 2022 at 08:01:23AM +0000, Eli Cohen wrote:
> > From: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Sent: Thursday, 22 September 2022 10:53
> > To: Eli Cohen <elic@xxxxxxxxxx>
> > Cc: Jason Wang <jasowang@xxxxxxxxxx>; si-wei.liu@xxxxxxxxxx; Parav
> > Pandit <parav@xxxxxxxxxx>; wuzongyong@xxxxxxxxxxxxxxxxx;
> > virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > eperezma@xxxxxxxxxx; lingshan.zhu@xxxxxxxxx; gdawar@xxxxxxxxxx;
> > lulu@xxxxxxxxxx; xieyongji@xxxxxxxxxxxxx
> > 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@xxxxxxxxxx>
> > > > Sent: Thursday, 22 September 2022 10:30
> > > > To: Eli Cohen <elic@xxxxxxxxxx>
> > > > Cc: Jason Wang <jasowang@xxxxxxxxxx>; si-wei.liu@xxxxxxxxxx; Parav
> > > > Pandit <parav@xxxxxxxxxx>; wuzongyong@xxxxxxxxxxxxxxxxx;
> > > > virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > > eperezma@xxxxxxxxxx; lingshan.zhu@xxxxxxxxx; gdawar@xxxxxxxxxx;
> > > > lulu@xxxxxxxxxx; xieyongji@xxxxxxxxxxxxx
> > > > 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@xxxxxxxxxx>
> > > > > > Sent: Thursday, 22 September 2022 5:43
> > > > > > To: mst@xxxxxxxxxx; jasowang@xxxxxxxxxx
> > > > > > Cc: Eli Cohen <elic@xxxxxxxxxx>; si-wei.liu@xxxxxxxxxx; Parav Pandit
> > > > > > <parav@xxxxxxxxxx>; wuzongyong@xxxxxxxxxxxxxxxxx;
> > > > > > virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx;
> > > > > > eperezma@xxxxxxxxxx; lingshan.zhu@xxxxxxxxx;
> > gdawar@xxxxxxxxxx;
> > > > > > lulu@xxxxxxxxxx; xieyongji@xxxxxxxxxxxxx
> > > > > > 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@xxxxxxxxxx>
> > > > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > > > > ---
> > > > > > 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
> > > > >
> > >
>

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Previous message: Paolo Abeni: "Re: [PATCH] Do not name control queue for virtio-net"
In reply to: Eli Cohen: "RE: [PATCH V2 2/3] vdpa_sim_net: support feature provisioning"
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