linux-kernel - Re: [PATCH v11 04/12] x86/mm: get INVLPGB count max from CPUID

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Message-ID: <20250219115626.GMZ7XG6s-5ftg1XLoZ@fat_crate.local>
Date: Wed, 19 Feb 2025 12:56:26 +0100
From: Borislav Petkov <bp@...en8.de>
To: Rik van Riel <riel@...riel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org,
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
	nadav.amit@...il.com, thomas.lendacky@....com, kernel-team@...a.com,
	linux-mm@...ck.org, akpm@...ux-foundation.org, jackmanb@...gle.com,
	jannh@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com,
	Manali Shukla <Manali.Shukla@....com>
Subject: Re: [PATCH v11 04/12] x86/mm: get INVLPGB count max from CPUID

On Thu, Feb 13, 2025 at 11:13:55AM -0500, Rik van Riel wrote:
> The CPU advertises the maximum number of pages that can be shot down
> with one INVLPGB instruction in the CPUID data.
> 
> Save that information for later use.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> Tested-by: Manali Shukla <Manali.Shukla@....com>
> Tested-by: Brendan Jackman <jackmanb@...gle.com>
> Tested-by: Michael Kelley <mhklinux@...look.com>
> ---
>  arch/x86/Kconfig.cpu               | 5 +++++
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/include/asm/tlbflush.h    | 7 +++++++
>  arch/x86/kernel/cpu/amd.c          | 8 ++++++++
>  4 files changed, 21 insertions(+)
> 
> diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
> index 2a7279d80460..abe013a1b076 100644
> --- a/arch/x86/Kconfig.cpu
> +++ b/arch/x86/Kconfig.cpu
> @@ -395,6 +395,10 @@ config X86_VMX_FEATURE_NAMES
>  	def_bool y
>  	depends on IA32_FEAT_CTL
>  
> +config X86_BROADCAST_TLB_FLUSH
> +	def_bool y
> +	depends on CPU_SUP_AMD && 64BIT
> +
>  menuconfig PROCESSOR_SELECT
>  	bool "Supported processor vendors" if EXPERT
>  	help
> @@ -431,6 +435,7 @@ config CPU_SUP_CYRIX_32
>  config CPU_SUP_AMD
>  	default y
>  	bool "Support AMD processors" if PROCESSOR_SELECT
> +	select X86_BROADCAST_TLB_FLUSH

CPU_SUP_AMD selects X86_BROADCAST_TLB_FLUSH which depends on CPU_SUP_AMD which
selects X86_BROADCAST_TLB_FLUSH which depends on CPU_SUP_AMD...

Why do you really need yet another Kconfig symbol? Just whack
X86_BROADCAST_TLB_FLUSH - it'll be enabled by default on everything anyway.

> @@ -1139,6 +1141,12 @@ static void cpu_detect_tlb_amd(struct cpuinfo_x86 *c)
>  		tlb_lli_2m[ENTRIES] = eax & mask;
>  
>  	tlb_lli_4m[ENTRIES] = tlb_lli_2m[ENTRIES] >> 1;
> +
> +	/* Max number of pages INVLPGB can invalidate in one shot */
> +	if (boot_cpu_has(X86_FEATURE_INVLPGB)) {
> +		cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
> +		invlpgb_count_max = (edx & 0xffff) + 1;
> +	}

get_cpu_cap() already reads that leaf. You don't need to do it here again.

-- 
Regards/Gruss,
    Boris.

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