Re: [RFC PATCH V4] pci: virtio_pci: Add SR-IOV support for virtio_pci devices

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

On Mon, Feb 26, 2018 at 02:38:01PM -0800, Alexander Duyck wrote:
> On Mon, Feb 26, 2018 at 2:32 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Mon, Feb 26, 2018 at 07:26:14AM -0800, Alexander Duyck wrote:
> >> On Sun, Feb 25, 2018 at 8:48 PM, Mark Rustad <mark.d.rustad@intel.com> wrote:
> >> > Hardware-realized virtio_pci devices can implement SR-IOV, so this
> >> > patch enables its use. The device in question is an upcoming Intel
> >> > NIC that implements both a virtio_net PF and virtio_net VFs. These
> >> > are hardware realizations of what has been up to now been a software
> >> > interface.
> >> >
> >> > The device in question has the following 4-part PCI IDs:
> >> >
> >> > PF: vendor: 1af4 device: 1041 subvendor: 8086 subdevice: 15fe
> >> > VF: vendor: 1af4 device: 1041 subvendor: 8086 subdevice: 05fe
> >> >
> >> > The patch needs no check for device ID, because the callback will
> >> > never be made for devices that do not assert the capability or
> >> > when run on a platform incapable of SR-IOV.
> >> >
> >> > One reason for this patch is because the hardware requires the
> >> > vendor ID of a VF to be the same as the vendor ID of the PF that
> >> > created it. So it seemed logical to simply have a fully-functioning
> >> > virtio_net PF create the VFs. This patch makes that possible.
> >> >
> >> > Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
> >> > Reviewed-by: Alexander Duyck <alexander.h.duyck@intel.com>
> >>
> >> Mark,
> >>
> >> In the future please don't put my "Reviewed-by" on a patch that I
> >> haven't reviewed. I believe I reviewed one of the earlier patches, but
> >> I hadn't reviewed this version.
> >>
> >> Also, after thinking about it over the weekend we may want to look at
> >> just coming up with a truly "generic" solution that is applied to
> >> SR-IOV capable devices that don't have a SR-IOV capable driver loaded
> >> on them. That would allow us to handle the uio, vfio, pci-stub, and
> >> virtio cases all in one fell swoop. I think us going though and
> >> modifying one patch at a time to do this kind of thing isn't going to
> >> scale.
> >
> > uio really can't support VFs properly - without proper IOMMU
> > support any MSIs can corrupt kernel memory, and VFs are
> > limited to MSIs.
> 
> UIO wasn't being run on the VFs, it was just running the PF.

I see. That's fine then.

> The point
> is that there have been about 4 attempts, including this one, to add
> SR-IOV support to drivers that don't actually do any VF management
> internally. They were just being used as a shim so that they could add
> the sriov_configure function to a driver that would load on the PF.
> 
> If we make the solution generic I think it should turn out pretty
> clean. Most of the work just needs to happen in the sysfs function for
> storing the value that is written to sriov_numvfs. I'm working with
> Mark and a few other people now to get this addressed and I hope that
> we can have a patch available shortly.
> 
> Thanks.
> 
> - Alex