linux-kernel - Re: `AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y` causes AMDGPU to fail on Ryzen: amdgpu: SME is not compatible with RAVEN

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Date:   Mon, 11 Oct 2021 08:27:35 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>, Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Alex Deucher <alexdeucher@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org
Subject: Re: `AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y` causes AMDGPU to fail on
 Ryzen: amdgpu: SME is not compatible with RAVEN

On 10/11/21 8:11 AM, Borislav Petkov wrote:
> On Mon, Oct 11, 2021 at 03:05:33PM +0200, Paul Menzel wrote:
>> I think, the IOMMU is enabled on the MSI B350M MORTAR, but otherwise, yes
>> this looks fine. The help text could also be updated to mention problems
>> with AMD Raven devices.
> 
> This is not only about Raven GPUs but, as Alex explained, pretty much
> about every device which doesn't support a 48 bit DMA mask. I'll expand
> that aspect in the changelog.

In general, non-GPU devices that don't support a 48-bit DMA mask work fine 
(assuming they have set their DMA mask appropriately). It really depends 
on whether SWIOTLB will be able to satisfy the memory requirements of the 
driver when the IOMMU is not enabled or in passthrough mode. Since GPU 
devices need/use a lot of memory, that becomes a problem.

Thanks,
Tom

>