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Subject: Re: [PATCH 0/2] iommu/amd: Fix IOMMUv2 devices when SME is active
To:     "jroedel@suse.de" <jroedel@suse.de>,
        "Deucher, Alexander" <Alexander.Deucher@amd.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "Huang, Ray" <Ray.Huang@amd.com>,
        "Koenig, Christian" <Christian.Koenig@amd.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Felix Kuehling <felix.kuehling@amd.com>
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Date:   Fri, 28 Aug 2020 09:54:59 -0400
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Am 2020-08-28 um 9:46 a.m. schrieb jroedel@suse.de:
> On Wed, Aug 26, 2020 at 03:25:58PM +0000, Deucher, Alexander wrote:
>>> Alex, do you know if anyone has tested amdgpu on an APU with SME
>>> enabled? Is this considered something we support?
>> It's not something we've tested.  I'm not even sure the GPU portion of
>> APUs will work properly without an identity mapping.  SME should work
>> properly with dGPUs however, so this is a proper fix for them.  We
>> don't use the IOMMUv2 path on dGPUs at all.
> Is it possible to make the IOMMUv2 paths optional on iGPUs as well when
> SME is active (or better, when the GPU is not identity mapped)?

Yes, we're working on this. IOMMUv2 is only needed for KFD. It's not
needed for graphics. And we're making it optional for KFD as well.

The question Alex and I raised here is more general. We may have some
assumptions in the amdgpu driver that are broken when the framebuffer is
not identity mapped. This would break the iGPU in a more general sense,
regardless of KFD and IOMMUv2. In that case, we don't really need to
worry about breaking KFD because we have a much bigger problem.

Regards,
  Felix


>
> Regards,
>
> 	Joerg