linux-kernel - Re: [PATCH v2] x86/mtrr: Check if fixed-range MTRR exists in mtrr_save_fixed

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Message-ID: <20250509173225.GDaB48KZvZSA9QLUaR@fat_crate.local>
Date: Fri, 9 May 2025 19:32:25 +0200
From: Borislav Petkov <bp@...en8.de>
To: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Bernhard Kaindl <bk@...e.de>,
	Andi Kleen <ak@...ux.intel.com>, Li Fei <fei1.li@...el.com>,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/mtrr: Check if fixed-range MTRR exists in
 mtrr_save_fixed_ranges()

On Fri, May 09, 2025 at 05:06:33PM +0000, Jiaqing Zhao wrote:
> When suspending, save_processor_state() calls mtrr_save_fixed_ranges()
> to save fixed-range MTRRs. On platforms without fixed-range MTRRs,
> accessing these MSRs will trigger unchecked MSR access error. Make
> sure fixed-range MTRRs are supported before access to prevent such
> error.
> 
> Since mtrr_state.have_fixed is only set when MTRRs are present and
> enabled, checking the CPU feature flag in mtrr_save_fixed_ranges()
> is unnecessary.
> 
> Fixes: 3ebad5905609 ("[PATCH] x86: Save and restore the fixed-range MTRRs of the BSP when suspending")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>

Next question: this is CC:stable, meaning it'll go to Linus now.

What exactly is it fixing?

Because the patch in Fixes: is from 2007. :-\

-- 
Regards/Gruss,
    Boris.

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