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

[Alexander Duyck <alexander.duyck@gmail.com>]

On Fri, Mar 16, 2018 at 9:34 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, Mar 15, 2018 at 11:42:41AM -0700, Alexander Duyck wrote:
>> From: Alexander Duyck <alexander.h.duyck@intel.com>
>>
>> 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 <mark.d.rustad@intel.com>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
>
> 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. One of the reasons why Mark called out the
subvendor/subdevice was because that might be able to be used to
identify the specific hardware that is providing the SR-IOV feature so
in the future if it is added to virtio itself then you could exclude
devices like this by just limiting things based on subvendor/subdevice
IDs.

> Also, I am guessing that hardware implementations will want
> to add things like stong memory barriers - I guess we
> will add new feature bits for that too down the road?

That piece I don't have visibility into at this time. Perhaps Dan
might have more visibility into future plans on what this might need.

Thanks.

- Alex