RE: [PATCH 2/2] iommu/amd: Force identity mode for selected GPUs only

AMD General

> -----Original Message-----
> From: Limonciello, Mario <[email protected]>
> Sent: Tuesday, July 28, 2026 1:31 AM
> To: Hegde, Vasant <[email protected]>; Jason Gunthorpe
> <[email protected]>; Deucher, Alexander <[email protected]>;
> Kuehling, Felix <[email protected]>
> Cc: [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Suthikulpanit, Suravee
> <[email protected]>; [email protected]; Longia,
> Amandeep Kaur <[email protected]>
> Subject: Re: [PATCH 2/2] iommu/amd: Force identity mode for selected GPUs
> only
>
> +Felix
>
> On 7/27/26 23:52, Vasant Hegde wrote:
> > Mario,
> >
> >
> > On 7/27/2026 8:15 PM, Mario Limonciello wrote:
> >>
> >>
> >> On 7/26/26 23:19, Vasant Hegde wrote:
> >>>
> >>>
> >
> > .../...
> >
> >>>>
> >>>> I think this can probably be dropped now? There is no intersection
> >>>> of this old broken embedded GPU and a CPU that supports CC right?
> >>>
> >>>
> >>> I did consider dropping these two checks, but I was not entirely
> >>> sure. So I kept as is for now. Once these series settles and I can
> >>> go with next step of dropping these two checks.
> >>>
> >>> @Alex, @Mario, Any suggestions ?
> >>>
> >>
> >> The background comes from this series:
> >>
> >> https://lore.kernel.org/all/[email protected]/
> >
> >
> > Thanks for old link. So it looks like we are good to drop SME check?
>
> Yeah I think so.
>
> >
> > Also is it safe to assume SNP is not enabled on these platform and
> > drop that check? Anyway SNP requirement (which doesn't support
> > identity mapping) and APU requirement (needs identity mapping) is
> conflicting.
> >
>
> The current platforms I think this is a safe assumption.
>
> Felix,
>
> Can we revisit the requirement of identity mapping for APU?  Does it still hold
> with the current hardware and software?
>
> I'm wondering if we can just apply it to Raven and loosen up elsewhere and
> what gives if we do that.


This issue only applies to the early raven/picasso families.  The display hardware had some hardware addressing bug with IOVAs so it has to have IOVA = IOPA.  The rest of the GPU can handle IOVAs just fine. This was fixed on Renoir IIRC.

Alex