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

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Message-ID: <20250509104445.GBaB3cnZnqCy-Vv6CR@fat_crate.local>
Date: Fri, 9 May 2025 12:44:45 +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] x86/mtrr: Check if fixed-range MTRR exists in
 `mtrr_save_fixed_ranges`

On Fri, May 09, 2025 at 08:56:12AM +0000, Jiaqing Zhao wrote:
> When suspending, `save_processor_state` calls `mtrr_save_fixed_ranges`

Put () after the function names and drop the ``.

> to save fixed-range MTRRs. On platforms without MTRR or fixed-range
> MTRR support, accessing MTRR MSRs triggers unchecked MSR access error.
> Make sure fixed-range MTRR is supported before access to prevent such
> error.
> 
> 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>
> ---
>  arch/x86/kernel/cpu/mtrr/generic.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
> index e2c6b471d230..ca37b374d1b0 100644
> --- a/arch/x86/kernel/cpu/mtrr/generic.c
> +++ b/arch/x86/kernel/cpu/mtrr/generic.c
> @@ -593,7 +593,7 @@ static void get_fixed_ranges(mtrr_type *frs)
>  
>  void mtrr_save_fixed_ranges(void *info)
>  {
> -	if (boot_cpu_has(X86_FEATURE_MTRR))
> +	if (boot_cpu_has(X86_FEATURE_MTRR) && mtrr_state.have_fixed)

Does it work too if you check only mtrr_state.have_fixed?

Without the feature check...

-- 
Regards/Gruss,
    Boris.

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