Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3

[Jason Gunthorpe]

On Thu, Feb 06, 2025 at 05:10:32PM +0000, Daniel P. Berrangé wrote:
> On Thu, Feb 06, 2025 at 01:02:38PM -0400, Jason Gunthorpe wrote:
> > On Thu, Feb 06, 2025 at 03:07:06PM +0000, Shameerali Kolothum Thodi wrote:
> > > > If we set the physical/guest SMMU relationship directly, then at the
> > > > time the VFIO device is plugged, we can diagnose the incorrectly
> > > > placed VFIO device, and better reason about behaviour.
> > > 
> > > Agree.
> > 
> > Can you just take in a VFIO cdev FD reference on this command line:
> > 
> >  -device arm-smmuv3-accel,id=smmuv2,bus=pcie.2
> > 
> > And that will lock the pSMMU/vSMMU relationship?
> 
> We shouldn't assume any VFIO device exists in the QEMU cnofig at the time
> we realize the virtual ssmu. I expect the SMMU may be cold plugged, while
> the VFIO devices may be hot plugged arbitrarly later, and we should have
> the association initialized the SMMU is realized.

This is not supported kernel side, you can't instantiate a vIOMMU
without a VFIO device that uses it. For security.

Jason