linux-kernel - Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE

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Message-ID: <20210706195233.h6w4cm73oktfqpgz@habkost.net>
Date:   Tue, 6 Jul 2021 15:52:33 -0400
From:   Eduardo Habkost <ehabkost@...hat.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.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@...gle.com>,
        Joe Perches <joe@...ches.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID
 bits RTM and HLE

On Wed, Jun 09, 2021 at 02:14:39PM -0700, Pawan Gupta wrote:
> On CPUs that deprecated TSX, clearing the enumeration bits CPUID.RTM and
> CPUID.HLE may not be desirable in some corner cases. Like a saved guest
> would refuse to resume if it was saved before the microcode update
> that deprecated TSX.

Why is a global option necessary to allow those guests to be
resumed?  Why can't KVM_GET_SUPPORTED_CPUID always return the HLE
and RTM bits as supported when the host CPU has them?


> 
> Add a cmdline option "tsx=fake" to not clear CPUID bits even when the
> hardware always aborts TSX transactions.
> 
> Suggested-by: Tony Luck <tony.luck@...el.com>
> Suggested-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Tested-by: Neelima Krishnan <neelima.krishnan@...el.com>
[...]

-- 
Eduardo