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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <SJ1PR11MB608321F26D729A082BFC6FAEFCFE9@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Mon, 9 Jan 2023 21:25:32 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>, "Moger, Babu" <babu.moger@....com>
CC:     "corbet@....net" <corbet@....net>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "paulmck@...nel.org" <paulmck@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "quic_neeraju@...cinc.com" <quic_neeraju@...cinc.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "damien.lemoal@...nsource.wdc.com" <damien.lemoal@...nsource.wdc.com>,
        "songmuchun@...edance.com" <songmuchun@...edance.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "jpoimboe@...nel.org" <jpoimboe@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        "pawan.kumar.gupta@...ux.intel.com" 
        <pawan.kumar.gupta@...ux.intel.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "daniel.sneddon@...ux.intel.com" <daniel.sneddon@...ux.intel.com>,
        "sandipan.das@....com" <sandipan.das@....com>,
        "james.morse@....com" <james.morse@....com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Eranian, Stephane" <eranian@...gle.com>,
        "christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "quic_jiles@...cinc.com" <quic_jiles@...cinc.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>
Subject: RE: [PATCH v11 04/13] x86/cpufeatures: Add Bandwidth Monitoring Event
 Configuration feature flag

>> 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.
>
> What would be the actual, real-life use case where the presence of those flags
> in /proc/cpuinfo is really needed?

It feels like the old "rule" was "make it visible in /proc/cpuid" unless there was some
good reason NOT to do it.  But that has resulted in the "flags" line getting ridiculously
long and hard for humans to read (141 fields with 926 bytes on my Skylake, more on
more modern CPUs).

For RDT I don't see a lot of value in knowing that a feature is present ... all of them
have parameters on how many things they can control/monitor ... so you have to
either go parse the CPUID leaves, or just mount /sys/fs/resctrl and look in the "info"
directory to get the extra information you need to do anything with RDT.

I don't know if we'd break anything if we dropped:

  cat_l3 cdp_l3 mba cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local

from /proc/cpuinfo.

Perhaps the "rule" should be written in Documentation/{somewhere}?

-Tony