linux-kernel - Re: [PATCH v6 11/16] x86/mtrr: construct a memory map with cache modes

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Date:   Tue, 9 May 2023 13:47:47 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.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>
Subject: Re: [PATCH v6 11/16] x86/mtrr: construct a memory map with cache
 modes

On 09.05.23 13:36, Borislav Petkov wrote:
> On Tue, May 02, 2023 at 02:09:26PM +0200, Juergen Gross wrote:
>> @@ -841,6 +1137,10 @@ static void generic_set_mtrr(unsigned int reg, unsigned long base,
>>   
>>   	cache_enable();
>>   	local_irq_restore(flags);
>> +
>> +	/* On the first CPU rebuild the cache mode memory map. */
>> +	if (smp_processor_id() == cpumask_first(cpu_online_mask))
>> +		rebuild_map();
> 
> I still don't like this. Anything against doing this instead?

No, Should be fine. Apart from ...

> 
> ---
> diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
> index 163dca53796c..e69c8c56897f 100644
> --- a/arch/x86/kernel/cpu/mtrr/generic.c
> +++ b/arch/x86/kernel/cpu/mtrr/generic.c
> @@ -458,8 +458,11 @@ static void map_add_var(void)
>    * removals of registers, which are complicated to handle without rebuild of
>    * the map.
>    */
> -static void rebuild_map(void)
> +void rebuild_map(void)
>   {
> +	if (mtrr_if != &generic_mtrr_ops)
> +		return;
> +
>   	cache_map_n = cache_map_fixed;
>   
>   	map_add_var();
> @@ -1127,10 +1130,6 @@ static void generic_set_mtrr(unsigned int reg, unsigned long base,
>   
>   	cache_enable();
>   	local_irq_restore(flags);
> -
> -	/* On the first CPU rebuild the cache mode memory map. */
> -	if (smp_processor_id() == cpumask_first(cpu_online_mask))
> -		rebuild_map();
>   }
>   
>   int generic_validate_add_page(unsigned long base, unsigned long size,
> diff --git a/arch/x86/kernel/cpu/mtrr/legacy.c b/arch/x86/kernel/cpu/mtrr/legacy.c
> index d25882fcf181..30a3d51d06e0 100644
> --- a/arch/x86/kernel/cpu/mtrr/legacy.c
> +++ b/arch/x86/kernel/cpu/mtrr/legacy.c
> @@ -67,6 +67,7 @@ static void mtrr_restore(void)
>   				     mtrr_value[i].ltype);
>   		}
>   	}
> +	rebuild_map();

... this call not being needed at all. We can reach this point only for
mtrr_if != &generic_mtrr_ops.


Juergen

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