linux-kernel - Re: [PATCH 1/4] x86/msr: Define new bits in TSX_FORCE

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Date:   Fri, 11 Jun 2021 10:39:43 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tony Luck <tony.luck@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kyung Min Park <kyung.min.park@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Krish Sadhukhan <krish.sadhukhan@...cle.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Joerg Roedel <jroedel@...e.de>,
        Victor Ding <victording@...gle.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        Anthony Steinhauser <asteinhauser@...gle.com>,
        Anand K Mistry <amistry@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...ogle.com>,
        Joe Perches <joe@...ches.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/4] x86/msr: Define new bits in TSX_FORCE_ABORT MSR

On Wed, Jun 09, 2021 at 01:58:02PM -0700, Pawan Gupta wrote:
> Intel client processors that support IA32_TSX_FORCE_ABORT MSR related to
> perf counter interaction [1] received a microcode update that deprecates
> Transactional Synchronization Extension (TSX) feature. MSR
> IA32_TSX_FORCE_ABORT bit FORCE_ABORT_RTM now defaults to 1, writes to
> this bit are ignored. A new bit TSX_CPUID_CLEAR clears the TSX related
> CPUID bits.
> 
> Below is the summary of changes to IA32_TSX_FORCE_ABORT MSR:
> 
>   Bit 0: FORCE_ABORT_RTM (legacy bit, new default=1) Status bit that
>   indicates if RTM transactions are always aborted. This bit is
>   essentially !SDV_ENABLE_RTM(Bit 2). Writes to this bit are ignored.
> 
>   Bit 1: TSX_CPUID_CLEAR (new bit, default=0) When set, CPUID.HLE = 0
>   and CPUID.RTM = 0.
> 
>   Bit 2: SDV_ENABLE_RTM (new bit, default=0) When clear, XBEGIN will
>   always abort with EAX code 0. When set, XBEGIN will not be forced to
>   abort (but will always abort in SGX enclaves). This bit is intended to
>   be SDV-only. If this bit is set transactional atomicity correctness is

SDV?

>   not certain.
> 
> Performance monitoring counter 3 is usable in all cases, regardless of
> the value of above bits.
> 
> A new CPUID bit CPUID.RTM_ALWAYS_ABORT (CPUID 7.EDX[11]) is added to
> indicate the status of always abort behavior.
> 
> Define these new CPUID and MSR bits.
> 
> [1] Performance Monitoring Impact of Intel® Transactional Synchronization Extension Memory
>     http://cdrdv2.intel.com/v1/dl/getContent/604224

That link does not look stable enough to put in commit messages.
Besides, you've said it all in the commit message already.

-- 
Regards/Gruss,
    Boris.

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