Re: [PATCH v1 15/16] iommu/arm-smmu-v3: Add viommu cache invalidation support

Nicolin Chen
2024-08-19T18:54:29Z

On Mon, Aug 19, 2024 at 03:47:16PM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 19, 2024 at 11:38:22AM -0700, Nicolin Chen wrote:
> > On Mon, Aug 19, 2024 at 03:28:11PM -0300, Jason Gunthorpe wrote:
> > > On Mon, Aug 19, 2024 at 11:19:39AM -0700, Nicolin Chen wrote:
> > >
> > > > > But nesting enablment with out viommu is alot less useful than I had
> > > > > thought :(
> > > >
> > > > Actually, without viommu, the hwpt cache invalidate alone could
> > > > still support non-SVA case?
> > >
> > > That is what I thought, but doesn't the guest still have to invalidate
> > > the CD table entry # 0?
> >
> > I recall it doesn't. The CD cache invalidation is required in the
> > viommu invalidation for an SVA case where we need a PASID number
> > to specify CD to the substream. But the CD to the default stream
> > is only changed during a vSTE setup, and the host knows the PASID
> > number (=0)?
>
> I think that would subtly assume certain things about how the driver
> does ordering, ie the that CD table entry 0 is setup with the S1
> before we load it into the STE.
>
> Yes, the Linux driver does that now, but I don't think anyone should
> rely on that..

Oh that's true...

Thanks
Nicolin