[PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

[Tian, Kevin]

> From: Nicolin Chen <nicolinc at nvidia.com>
> Sent: Tuesday, May 6, 2025 10:54 AM
> 
> On Mon, May 05, 2025 at 02:08:07PM -0300, Jason Gunthorpe wrote:
> > On Wed, Apr 30, 2025 at 12:58:47AM -0700, Nicolin Chen wrote:
> >
> > > > ... and I just hit a problem with it - this is basically guest BDFn
> > > > and it works as long as I'm hotplugging the TEE-IO VF into an SNP VM
> > > > but does not when I pass through via the QEMU cmdline - bus numbers
> > > > are not assigned yet. So I have to postpone the vdevice allocation
> > > > till run time, did I miss something here? Thanks,
> > >
> > > I have a similar case with QEMU ARM64's VM: so vDEVICE on ARM is
> > > allocated at runtime as well because the BDF number isn't ready
> > > at the boot time.
> >
> > Oh that's ugly then.. So you'll need to add some kind of 'modify
> > sid/bdf' operation I think.
> 
> But the initial vDEVICE would be still unusable. Its BDF number is
> literally 0 in my case. It can't be used for SID-based invalidation
> nor the reverse vSID lookup for fault injection..
> 

Agree that it makes more sense to allocate vDEVICE at runtime until
it's assigned with a valid bus number. and destroy/recreation is
required when the bus number is changed.