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

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Message-ID: <b749384b7dea020880057359d06d4e9172c7aaec.camel@surriel.com>
Date: Wed, 19 Feb 2025 12:52:56 -0500
From: Rik van Riel <riel@...riel.com>
To: Borislav Petkov <bp@...en8.de>
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 Wed, 2025-02-19 at 12:56 +0100, Borislav Petkov wrote:
> 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.

Dave specifically asked me to do things that way.

> 
> > @@ -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.
> 
Should I modify get_cpu_cap() to store
c->x86_capabilities[CPUID_8000_0008_EDX] ?

Currently only the EBX data is stored there,
while invlpgb_count_max comes from EDX.

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