Re: [PATCH V1 vfio 9/9] vfio/virtio: Introduce a vfio driver over virtio devices

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Parav Pandit <parav@nvidia.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Maor Gottlieb <maorg@nvidia.com>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	Jason Gunthorpe <jgg@nvidia.com>, Jiri Pirko <jiri@nvidia.com>,
	Leon Romanovsky <leonro@nvidia.com>
Subject: Re: [PATCH V1 vfio 9/9] vfio/virtio: Introduce a vfio driver over virtio devices
Date: Thu, 26 Oct 2023 11:46:13 -0400	[thread overview]
Message-ID: <20231026112804-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <PH0PR12MB54819C408A120436010F608FDCDDA@PH0PR12MB5481.namprd12.prod.outlook.com>

On Thu, Oct 26, 2023 at 03:09:13PM +0000, Parav Pandit wrote:
> 
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Thursday, October 26, 2023 8:36 PM
> > 
> > On Thu, Oct 26, 2023 at 01:28:18PM +0000, Parav Pandit wrote:
> > >
> > > > From: Michael S. Tsirkin <mst@redhat.com>
> > > > Sent: Thursday, October 26, 2023 6:45 PM
> > >
> > > > > Followed by an open coded driver check for 0x1000 to 0x103f range.
> > > > > Do you mean windows driver expects specific subsystem vendor id of
> > 0x1af4?
> > > >
> > > > Look it up, it's open source.
> > >
> > > Those are not OS inbox drivers anyway.
> > > :)
> > 
> > Does not matter at all if guest has drivers installed.
> > Either you worry about legacy guests or not.
> > 
> So, Linux guests have inbox drivers, that we care about and they seems to be covered, right?
> 
> > 
> > > The current vfio driver is following the virtio spec based on legacy spec, 1.x
> > spec following the transitional device sections.
> > > There is no need to do something out of spec at this point.
> > 
> > legacy spec wasn't maintained properly, drivers diverged sometimes
> > significantly. what matters is installed base.
> 
> So if you know the subsystem vendor id that Windows expects, please share, so we can avoid playing puzzle game. :)
> It anyway can be reported by the device itself.

I don't know myself offhand. I just know it's not so simple. Looking at the source
for network drivers I see:

%kvmnet6.DeviceDesc%    = kvmnet6.ndi, PCI\VEN_1AF4&DEV_1000&SUBSYS_0001_INX_SUBSYS_VENDOR_ID&REV_00, PCI\VEN_1AF4&DEV_1000

So the drivers will:
A. bind with high priority to subsystem vendor ID used when drivers where built.
   popular drivers built and distributed for free by Red Hat have 1AF4
B. bind with low priority to any subsystem device/vendor id as long as
   vendor is 1af4 and device is 1000

My conclusions:
- you probably need a way to tweak subsystem vendor id in software
- default should probably be 1AF4 not whatever actual device uses

-- 
MST

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