linux-kernel - Re: [PATCH v13 02/14] x86/mm: get INVLPGB count max from CPUID

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Message-ID: <20250224120029.GDZ7xfXV3jMjnbdbGl@fat_crate.local>
Date: Mon, 24 Feb 2025 13:00:29 +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@....com, mingo@...nel.org,
	Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v13 02/14] x86/mm: get INVLPGB count max from CPUID

On Sun, Feb 23, 2025 at 02:48:52PM -0500, Rik van Riel wrote:
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 3da645139748..09463a2fb05f 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -183,6 +183,9 @@ static inline void cr4_init_shadow(void)
>  extern unsigned long mmu_cr4_features;
>  extern u32 *trampoline_cr4_features;
>  
> +/* How many pages can we invalidate with one INVLPGB. */

"... can be invalidated... "

Please use passive voice in your text: no "we" or "I", etc,
and describe your changes in imperative mood.

Bottom line is: personal pronouns are ambiguous in text, especially with
so many parties/companies/etc developing the kernel so let's avoid them
please.

Please check all your text.

> +extern u16 invlpgb_count_max;
> +
>  extern void initialize_tlbstate_and_flush(void);
>  
>  /*
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 54194f5995de..3e8180354303 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -29,6 +29,8 @@
>  
>  #include "cpu.h"
>  
> +u16 invlpgb_count_max __ro_after_init;
> +
>  static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
>  {
>  	u32 gprs[8] = { 0 };
> @@ -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;
> +	}
>  }

Ontop:

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 3e8180354303..7a72ef47a983 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -1143,10 +1143,8 @@ static void cpu_detect_tlb_amd(struct cpuinfo_x86 *c)
 	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;
-	}
+	if (cpu_has(c, X86_FEATURE_INVLPGB))
+		invlpgb_count_max = (cpuid_edx(0x80000008) & 0xffff) + 1;
 }
 
 static const struct cpu_dev amd_cpu_dev = {

-- 
Regards/Gruss,
    Boris.

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