Linux Virtualization - Oct 2023 - [PATCH V1 vfio 9/9] vfio/virtio: Introduce a vfio driver over virtio devices

> From: Michael S. Tsirkin <mst at 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 at 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.

On Thu, Oct 26, 2023 at 03:09:13PM +0000, Parav Pandit
wrote:
> 
> > From: Michael S. Tsirkin <mst at 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 at 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