Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 6 Oct 2021 15:46:44 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Alex Deucher <alexdeucher@gmail.com>
Cc:     Paul Menzel <pmenzel@molgen.mpg.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        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
Message-ID: <YV2oxBw4I4kizvhF@zn.tnic>
References: <8bbacd0e-4580-3194-19d2-a0ecad7df09c@molgen.mpg.de>
 <CADnq5_ONNvuvTbiJDFfRwfnPUBeAqPmDJRmESDYG_7CymikJpQ@mail.gmail.com>
 <YV1vcKpRvF9WTwAo@zn.tnic>
 <CADnq5_N5+SEW4JyXLc=FdSHnSbXrGKWjEw4vW1Jxv9-KdWf+Jg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CADnq5_N5+SEW4JyXLc=FdSHnSbXrGKWjEw4vW1Jxv9-KdWf+Jg@mail.gmail.com>
Precedence: bulk

On Wed, Oct 06, 2021 at 09:23:22AM -0400, Alex Deucher wrote:
> There could be some OEM systems that disable the IOMMU on the platform
> and don't provide a switch in the bios to enable it.  The GPU driver
> will still work in that case, it will just not be able to enable KFD
> support for ROCm compute.  SME won't work for most devices in that
> case however since most devices have a DMA mask too small to handle
> the C bit for encryption.  SME should be dependent on IOMMU being
> enabled.

Yeah, I'd let you hash this out with Tom.

> I'm not an SME expert, but I thought that that was already the case.

Yeah, I think Paul wants this:

---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b79e88ee6627..e94c2df7a043 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1518,7 +1518,6 @@ config AMD_MEM_ENCRYPT
 
 config AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
 	bool "Activate AMD Secure Memory Encryption (SME) by default"
-	default y
 	depends on AMD_MEM_ENCRYPT
 	help
 	  Say yes to have system memory encrypted by default if running on

---

The reason we did this is so that you don't want to supply
mem_encrypt=on on the cmdline but didn't anticipate any such fun with
some devices.

> We just added the error condition in the GPU driver to prevent the
> driver from loading when the user forced SME on.  IIRC, there were
> users that cared more about SME than graphics support.

Well, it's a distro kernel so we should at least try to make everyone
happy. :)

-- 
Regards/Gruss,
    Boris.

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