RE: [PATCH v8 01/13] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

["Moger, Babu" <Babu.Moger@amd.com>]

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[AMD Official Use Only - General]

Hi Fenghua,

> -----Original Message-----
> From: Yu, Fenghua <fenghua.yu@intel.com>
> Sent: Wednesday, November 23, 2022 12:22 PM
> To: Moger, Babu <Babu.Moger@amd.com>; corbet@lwn.net; Chatre, Reinette
> <reinette.chatre@intel.com>; tglx@linutronix.de; mingo@redhat.com;
> bp@alien8.de
> Cc: dave.hansen@linux.intel.com; x86@kernel.org; hpa@zytor.com;
> paulmck@kernel.org; akpm@linux-foundation.org; quic_neeraju@quicinc.com;
> rdunlap@infradead.org; damien.lemoal@opensource.wdc.com;
> songmuchun@bytedance.com; peterz@infradead.org; jpoimboe@kernel.org;
> pbonzini@redhat.com; Bae, Chang Seok <chang.seok.bae@intel.com>;
> pawan.kumar.gupta@linux.intel.com; jmattson@google.com;
> daniel.sneddon@linux.intel.com; Das1, Sandipan <Sandipan.Das@amd.com>;
> Luck, Tony <tony.luck@intel.com>; james.morse@arm.com; linux-
> doc@vger.kernel.org; linux-kernel@vger.kernel.org; bagasdotme@gmail.com;
> Eranian, Stephane <eranian@google.com>
> Subject: RE: [PATCH v8 01/13] x86/cpufeatures: Add Slow Memory Bandwidth
> Allocation feature flag
> 
> Hi, Babu,
> 
> > diff --git a/arch/x86/include/asm/cpufeatures.h
> > b/arch/x86/include/asm/cpufeatures.h
> > index aefd0816a333..d68b4c9c181d 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -305,6 +305,7 @@
> >  #define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB
> > during runtime firmware calls */
> >  #define X86_FEATURE_RSB_VMEXIT_LITE	(11*32+17) /* "" Fill RSB on
> VM
> > exit when EIBRS is enabled */
> >  #define X86_FEATURE_CALL_DEPTH		(11*32+18) /* "" Call depth
> > tracking for RSB stuffing */
> > +#define X86_FEATURE_SMBA		(11*32+19) /* Slow Memory
> > Bandwidth Allocation */
> >
> >  /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
> >  #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI
> > instructions */
> > diff --git a/arch/x86/kernel/cpu/scattered.c
> > b/arch/x86/kernel/cpu/scattered.c index fc01f81f6e2a..5a5f17ed69a2
> > 100644
> > --- a/arch/x86/kernel/cpu/scattered.c
> > +++ b/arch/x86/kernel/cpu/scattered.c
> > @@ -44,6 +44,7 @@ static const struct cpuid_bit cpuid_bits[] = {
> >  	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
> >  	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
> >  	{ X86_FEATURE_MBA,		CPUID_EBX,  6, 0x80000008, 0 },
> > +	{ X86_FEATURE_SMBA,		CPUID_EBX,  2, 0x80000020, 0 },
> >  	{ X86_FEATURE_PERFMON_V2,	CPUID_EAX,  0, 0x80000022, 0 },
> >  	{ X86_FEATURE_AMD_LBR_V2,	CPUID_EAX,  1, 0x80000022, 0 },
> >  	{ 0, 0, 0, 0, 0 }
> >
> 
> Shouldn't X86_FEATURE_SMBA depend on X86_FEATURE_MBA? Need to add
> the dependency in cpuid-deps.c

I won't consider them as dependents. They both have separate CPUID bits and MSRs.
Thanks
Babu

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