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

From: Alexander Duyck <alexander.duyck@gmail.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, "Daly, Dan" <dan.daly@intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	"Duyck, Alexander H" <alexander.h.duyck@intel.com>,
	linux-pci@vger.kernel.org, virtio-dev@lists.oasis-open.org,
	kvm@vger.kernel.org, Netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-nvme@lists.infradead.org,
	Keith Busch <keith.busch@intel.com>,
	netanel@amazon.com, Don Dutile <ddutile@redhat.com>,
	Maximilian Heyne <mheyne@amazon.de>,
	"Wang, Liang-min" <liang-min.wang@intel.com>,
	"Rustad, Mark D" <mark.d.rustad@intel.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Christoph Hellwig <hch@lst.de>,
	dwmw@amazon.co.uk
Subject: Re: [virtio-dev] [pci PATCH v7 2/5] virtio_pci: Add support for unmanaged SR-IOV on virtio_pci devices
Date: Fri, 16 Mar 2018 09:40:34 -0700	[thread overview]
Message-ID: <CAKgT0UfgZ2gAdiAbCe4MTOr3o9cqq1q-mykCQsw68p2F-QEC8g@mail.gmail.com> (raw)
In-Reply-To: <20180316183042-mutt-send-email-mst@kernel.org>

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