linux-kernel - Re: [PATCH v11 04/13] x86/cpufeatures: Add Bandwidth Monitoring Event Configuration feature flag

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Message-ID: <5afd0a7c-3fbe-dfea-f1b4-2fc35fbb4f13@amd.com>
Date:   Mon, 9 Jan 2023 13:49:09 -0600
From:   "Moger, Babu" <babu.moger@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     corbet@....net, reinette.chatre@...el.com, tglx@...utronix.de,
        mingo@...hat.com, fenghua.yu@...el.com,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        paulmck@...nel.org, akpm@...ux-foundation.org,
        quic_neeraju@...cinc.com, rdunlap@...radead.org,
        damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
        peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
        chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
        jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
        sandipan.das@....com, tony.luck@...el.com, james.morse@....com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
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        christophe.leroy@...roup.eu, jarkko@...nel.org,
        adrian.hunter@...el.com, quic_jiles@...cinc.com,
        peternewman@...gle.com
Subject: Re: [PATCH v11 04/13] x86/cpufeatures: Add Bandwidth Monitoring Event
 Configuration feature flag

Hi Boris,

On 1/9/23 12:58, Borislav Petkov wrote:
> On Mon, Jan 09, 2023 at 10:43:56AM -0600, Babu Moger wrote:
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index 00045123f418..db5287c06b65 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -308,6 +308,7 @@
>>  #define X86_FEATURE_CALL_DEPTH		(11*32+19) /* "" Call depth tracking for RSB stuffing */
>>  #define X86_FEATURE_MSR_TSX_CTRL	(11*32+20) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
>>  #define X86_FEATURE_SMBA		(11*32+21) /* Slow Memory Bandwidth Allocation */
>> +#define X86_FEATURE_BMEC		(11*32+22) /* Bandwidth Monitoring Event Configuration */
> If those flags are meant only for internal kernel code use - it looks like it -
> and userspace doesn't care, pls put "" in front of both in the comment like the
> others above them do.

All the QoS(or RDT) features are visible so far. If we make them visible,
users can easily figure out if this specific feature is supported or not.

There is some benefit if we make it visible. What do you think?

Thanks

Babu