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

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.

-- 
MST

> 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?