linux-kernel - [PING] Re: [PATCH v3] x86/mtrr: Check if fixed MTRRs exist before saving them

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Date: Mon, 1 Apr 2024 14:19:35 -0700
From: Andi Kleen <ak@...ux.intel.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
Subject: [PING] Re: [PATCH v3] x86/mtrr: Check if fixed MTRRs exist before
 saving them

On Wed, Feb 28, 2024 at 04:19:52PM -0800, Andi Kleen wrote:
> MTRRs have a obsolete fixed variant for fine grained
> caching control of the 640K-1MB region. This fixed variant has a
> separate capability bit in the MTRR capability MSR. The MTRR code
> checks this capability bit before trying to access the fixed MTRR MSRs,
> except in one place. This patch fixes this place to also
> check the capability.
> 
> Otherwise there will be a WARN_ON when the respective MSRS don't exist.
> 
> Fixes: 2b1f6278d77c ("[PATCH] x86: Save the MTRRs of the BSP before booting an AP")
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>

Ping!

> 
> ---
> 
> v2: Add Fixes tag and expand description.
> v3: Expand description
> ---
>  arch/x86/kernel/cpu/mtrr/mtrr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
> index 767bf1c71aad..2a2fc14955cd 100644
> --- a/arch/x86/kernel/cpu/mtrr/mtrr.c
> +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
> @@ -609,7 +609,7 @@ void mtrr_save_state(void)
>  {
>  	int first_cpu;
>  
> -	if (!mtrr_enabled())
> +	if (!mtrr_enabled() || !mtrr_state.have_fixed)
>  		return;
>  
>  	first_cpu = cpumask_first(cpu_online_mask);
> -- 
> 2.43.0
>