Re: [virtio-dev] [pci PATCH v7 2/5] virtio_pci: Add support for unmanaged SR-IOV on virtio_pci devices

On Tue, Apr 03, 2018 at 10:32:00AM -0700, Alexander Duyck wrote:

On Tue, Apr 3, 2018 at 6:12 AM, Michael S. Tsirkin [off-list ref] wrote:

quoted

On Fri, Mar 16, 2018 at 09:40:34AM -0700, Alexander Duyck wrote:

quoted

On Fri, Mar 16, 2018 at 9:34 AM, Michael S. Tsirkin [off-list ref] wrote:

quoted

On Thu, Mar 15, 2018 at 11:42:41AM -0700, Alexander Duyck wrote:

quoted

From: Alexander Duyck <redacted>

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 currently 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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mark Rustad <redacted>
Signed-off-by: Alexander Duyck <redacted>

So if and when virtio PFs can manage the VFs, then we can
add a feature bit for that?
Seems reasonable.

Yes. If nothing else you may not even need a feature bit depending on
how things go.

OTOH if the interface is changed in an incompatible way,
and old Linux will attempt to drive the new device
since there is no check.

I think we should add a feature bit right away.

I'm not sure why you would need a feature bit. The capability is
controlled via PCI configuration space. If it is present the device
has the capability. If it is not then it does not.

Basically if the PCI configuration space is not present then the sysfs
entries will not be spawned and nothing will attempt to use this
function.

- ALex

It's about compability with older guests which ignore the
capability.

The feature is thus helpful so host knows whether guest supports VFs.


-- 
MSR