linux-kernel - Re: [PATCH 3/4] x86/tsx: Clear CPUID bits when TSX always force aborts

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Message-ID: <20210611213622.n3rlgzwe7c6q7lfu@gupta-dev2.localdomain>
Date:   Fri, 11 Jun 2021 14:36:22 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
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>, Joe Perches <joe@...ches.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 3/4] x86/tsx: Clear CPUID bits when TSX always force
 aborts

On 11.06.2021 12:03, Borislav Petkov wrote:
>On Wed, Jun 09, 2021 at 02:13:38PM -0700, Pawan Gupta wrote:
>> @@ -114,6 +127,26 @@ void __init tsx_init(void)
>>  			tsx_ctrl_state = TSX_CTRL_ENABLE;
>>  	}
>>
>> +	/*
>> +	 * Hardware will always abort a TSX transaction if both CPUID bits
>> +	 * RTM_ALWAYS_ABORT and TSX_FORCE_ABORT are enumerated.  In this case it
>> +	 * is better not to enumerate CPUID.RTM and CPUID.HLE bits. Clear them
>> +	 * here.
>> +	 */
>> +	if (boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) &&
>> +	    boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT)) {
>> +		tsx_ctrl_state = TSX_CTRL_RTM_ALWAYS_ABORT;
>> +		tsx_clear_cpuid();
>> +		setup_clear_cpu_cap(X86_FEATURE_RTM);
>> +		setup_clear_cpu_cap(X86_FEATURE_HLE);
>> +		return;
>> +	}
>
>Why isn't this happening as the first thing on entry in that tsx_init()
>function? IOW, there's no point to noodle through cmdline options etc if
>the hardware will always abort transactions.

Because the next patch is adding tsx=fake cmdline, for that this code
needs to be executed after cmdline parsing. I wanted to avoid the churn
to move this code between patches.

But, I see your comment for 4/4 i.e. tsx=fake may not be needed. It was
added after an internal test failure.

tsx=fake is really for a corner case and if that patch goes away it
would make sense to move the code in question here before cmdline
parsing.

Thanks,
Pawan