linux-kernel - Re: [PATCH] x86/cpu/amd: Remove dead code for TSEG region remapping

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Date:   Thu, 3 Dec 2020 17:44:11 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
        Kim Phillips <kim.phillips@....com>,
        Yazen Ghannam <yazen.ghannam@....com>, Pu Wen <puwen@...on.cn>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/cpu/amd: Remove dead code for TSEG region remapping

On Thu, Dec 03, 2020 at 11:14:06AM -0500, Arvind Sankar wrote:
> Do any of them have it mapped at all, regardless of the alignment? There
> seems to be nothing else in the kernel that ever looks at the TSEG MSR,
> so I would guess that it has to be non-RAM in the E820 map, otherwise
> nothing would prevent the kernel from allocating and using that space.

Ha, that's a very good question. If all those BIOSes from K8 onwards
would put the TSEG in a non-RAM area and after

  66520ebc2df3 ("x86, mm: Only direct map addresses that are marked as E820_RAM")

(great investigative work, btw, thanks for that!) then we can simply say
that that splitting is not needed anymore.

Maybe Tom can ask BIOS people whether they always did that - that being
to put the TSEG into a non-RAM area. I can boot my debug patch on my
boxes here but that doesn't mean a whole lot...

Thx.

-- 
Regards/Gruss,
    Boris.

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