Re: [PATCH v2 17/19] iommu/arm-smmu-v3: Add arm_smmu_viommu_cache_invalidate

Jason Gunthorpe
2024-09-14T14:52:40Z

On Fri, Sep 13, 2024 at 02:33:59AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Thursday, September 12, 2024 7:08 AM
> >
> > On Wed, Sep 11, 2024 at 08:13:01AM +0000, Tian, Kevin wrote:
> >
> > > Probably there is a good reason e.g. for simplification or better
> > > aligned with hw accel stuff. But it's not explained clearly so far.
> >
> > Probably the most concrete thing is if you have a direct assignment
> > invalidation queue (ie DMA'd directly by HW) then it only applies to a
> > single pIOMMU and invalidation commands placed there are unavoidably
> > limited in scope.
> >
> > This creates a representation problem, if we have a vIOMMU that spans
> > many pIOMMUs but invalidations do some subset how to do we model
> > that. Just saying the vIOMMU is linked to the pIOMMU solves this
> > nicely.
> >
>
> yes that is a good reason.
>
> btw do we expect the VMM to try-and-fail when deciding whether a
> new vIOMMU object is required when creating a new vdev?

I think there was some suggestion the getinfo could return this, but
also I think qemu needs to have a command line that matches physical
so maybe it needs some sysfs?

Jason