linux-kernel - Re: [PATCH 04/12] x86/mm: get INVLPGB count max from CPUID

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Message-ID: <20250102121511.GOZ3aDTzdz2-Q_PkaX@fat_crate.local>
Date: Thu, 2 Jan 2025 13:15:11 +0100
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	akpm@...ux-foundation.org, nadav.amit@...il.com,
	zhengqi.arch@...edance.com, linux-mm@...ck.org
Subject: Re: [PATCH 04/12] x86/mm: get INVLPGB count max from CPUID

On Mon, Dec 30, 2024 at 12:53:05PM -0500, Rik van Riel wrote:
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index f1fea506e20f..6c4d08f8f7b1 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -138,6 +138,10 @@ __visible unsigned long mmu_cr4_features __ro_after_init;
>  __visible unsigned long mmu_cr4_features __ro_after_init = X86_CR4_PAE;
>  #endif
>  
> +#ifdef CONFIG_CPU_SUP_AMD
> +u16 invlpgb_count_max __ro_after_init;
> +#endif

You can define this in amd.c and put the ifdeffery in the header. Something
like:

#ifdef CONFIG_CPU_SUP_AMD
extern u16 invlpgb_count_max __ro_after_init;
#else
#define invlpgb_count_max 0
#endif

or so and use it freely in the remaining places.

-- 
Regards/Gruss,
    Boris.

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