linux-kernel - Re: [PATCH v8 8/9] x86/mtrr: Avoid repeated save of MTRRs on boot-time CPU bringup

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Date:   Thu, 09 Feb 2023 19:31:16 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Usama Arif <usama.arif@...edance.com>, dwmw2@...radead.org,
        kim.phillips@....com
Cc:     arjan@...ux.intel.com, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, x86@...nel.org,
        pbonzini@...hat.com, paulmck@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
        thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
        fam.zheng@...edance.com, punit.agrawal@...edance.com,
        simon.evans@...edance.com, liangma@...ngbit.com,
        David Woodhouse <dwmw@...zon.co.uk>,
        Usama Arif <usama.arif@...edance.com>
Subject: Re: [PATCH v8 8/9] x86/mtrr: Avoid repeated save of MTRRs on
 boot-time CPU bringup

On Thu, Feb 09 2023 at 15:41, Usama Arif wrote:
>  void mtrr_save_state(void)
>  {
> +	static bool mtrr_saved;
>  	int first_cpu;
>  
>  	if (!mtrr_enabled())
>  		return;
>  
> +	if (system_state < SYSTEM_RUNNING) {
> +		if (!mtrr_saved) {
> +			mtrr_save_fixed_ranges(NULL);
> +			mtrr_saved = true;
> +		}
> +		return;
> +	}
> +
>  	first_cpu = cpumask_first(cpu_online_mask);
>  	smp_call_function_single(first_cpu, mtrr_save_fixed_ranges, NULL, 1);

So why is this relevant after the initial bringup? The BP MTRRs have
been saved already above, no?

Thanks,

        tglx