linux-kernel - Re: [PATCH v6 00/16] x86/mtrr: fix handling with PAT but without MTRR

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Date:   Tue, 9 May 2023 22:14:37 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hyperv@...r.kernel.org, linux-doc@...r.kernel.org,
        mikelley@...rosoft.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v6 00/16] x86/mtrr: fix handling with PAT but without MTRR

On Tue, May 02, 2023 at 02:09:15PM +0200, Juergen Gross wrote:
> This series tries to fix the rather special case of PAT being available
> without having MTRRs (either due to CONFIG_MTRR being not set, or
> because the feature has been disabled e.g. by a hypervisor).

More weird stuff. With the series:

[root@vh: ~> cat /proc/mtrr 
cat: /proc/mtrr: Input/output error

before:

[root@vh: ~> cat /proc/mtrr 
reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
reg02: base=0x0c0000000 ( 3072MB), size=  256MB, count=1: write-back
reg03: base=0x0ff000000 ( 4080MB), size=   16MB, count=1: write-protect

I think it wrongly determines that MTRRs are disabled by BIOS:

MTRRs disabled by BIOS
x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WP  UC- WT

which is obviously wrong.

But more debugging later.

-- 
Regards/Gruss,
    Boris.

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