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Date:   Wed, 6 Oct 2021 21:32:38 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Alex Deucher <alexdeucher@gmail.com>
Cc:     Tom Lendacky <thomas.lendacky@amd.com>,
        Paul Menzel <pmenzel@molgen.mpg.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>
Subject: 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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On Wed, Oct 06, 2021 at 02:21:40PM -0400, Alex Deucher wrote:
> And just another general comment, swiotlb + bounce buffers isn't
> really useful on GPUs.  You may have 10-100s of MBs of memory mapped
> long term into the GPU's address space for random access.  E.g., you
> may have buffers in system memory that the display hardware is
> actively scanning out of.  For GPUs you should really only enable SME
> if IOMMU is enabled in remapping mode.  But that is probably beyond
> the discussion here.

Right, but insights into how these things work (or don't work) together
are always welcome. And yes, as 2cc13bb4f59f says:

    "... The bounce buffer
    code has an upper limit of 256kb for the size of DMA
    allocations, which is too small for certain devices and
    causes them to fail."

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette