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

On Thu, Oct 26, 2023 at 12:40:04PM +0000, Parav Pandit
wrote:
> > From: Michael S. Tsirkin <mst at redhat.com>
> > Sent: Thursday, October 26, 2023 5:42 PM
> > 
> > On Thu, Oct 26, 2023 at 03:08:12PM +0300, Yishai Hadas wrote:
> > > > > Makes sense ?
> > > > So do I understand correctly that virtio dictates the
subsystem
> > > > device ID for all subsystem vendor IDs that implement a
legacy
> > > > virtio interface?  Ok, but this device didn't actually
implement a
> > > > legacy virtio interface.  The device itself is not
tranistional,
> > > > we're imposing an emulated transitional interface onto
it.  So did
> > > > the subsystem vendor agree to have their subsystem device ID
managed
> > > > by the virtio committee or might we create conflicts?  I
imagine we
> > > > know we don't have a conflict if we also virtualize the
subsystem vendor ID.
> > > >
> > > The non transitional net device in the virtio spec defined as the
> > > below tuple.
> > > T_A: VID=0x1AF4, DID=0x1040, Subsys_VID=FOO, Subsys_DID=0x40.
> > >
> > > And transitional net device in the virtio spec for a vendor FOO
is
> > > defined
> > > as:
> > > T_B: VID=0x1AF4,DID=0x1000,Subsys_VID=FOO, subsys_DID=0x1
> > >
> > > This driver is converting T_A to T_B, which both are defined by
the
> > > virtio spec.
> > > Hence, it does not conflict for the subsystem vendor, it is fine.
> > 
> > You are talking about legacy guests, what 1.X spec says about them is
much less
> > important than what guests actually do.
> > Check the INF of the open source windows drivers and linux code, at
least.
> 
> Linux legacy guest has,
> 
> static struct pci_device_id virtio_pci_id_table[] = {
>         { 0x1af4, PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 },
>         { 0 },
> };
> 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.

> 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.
:)
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.