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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Message-ID: <YV2oxBw4I4kizvhF@zn.tnic>
Date:   Wed, 6 Oct 2021 15:46:44 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Tom Lendacky <thomas.lendacky@....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 list <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 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