Re: [PATCH v4 22/28] iommu/arm-smmu-v3-kvm: Emulate CMDQ for host

Will Deacon
2025-09-17T15:01:41Z

On Wed, Sep 17, 2025 at 09:36:01AM -0300, Jason Gunthorpe wrote:
> On Tue, Sep 16, 2025 at 03:19:02PM +0000, Mostafa Saleh wrote:
>
> > I think the fix for the problem Will mentioned is to just use CMOs
> > before accessing the host structures, so that should be simple.
> > If it turns to be more complicated, I am happy to drop the support
> > for non-coherent devices from this series and we can add it later.
>
> I feel like it is easier/better to fix the driver to use cachable
> memory than to add CMOs to the pkvm side..

Hmm, but for non-coherent SMMU hardware (which sadly exists in
production), I don't think there's a way for firmware to tell the driver
that it needs to issue CMOs for the page-tables and the CDs but not the
other in-memory data structures (e.g. STEs). I suppose we could do it in
some pKVM-specific way, but then that's not really helping anybody else.

Will