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Date:   Tue, 6 Jul 2021 15:51:27 -0700
From:   Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To:     Eduardo Habkost <ehabkost@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Viresh Kumar <viresh.kumar@linaro.org>,
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Subject: Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID
 bits RTM and HLE
Message-ID: <20210706225127.kyn7amrln6ydfcig@gupta-dev2.localdomain>
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On 06.07.2021 17:19, Eduardo Habkost wrote:
>On Tue, Jul 6, 2021 at 5:15 PM Pawan Gupta
><pawan.kumar.gupta@linux.intel.com> wrote:
>>
>> On 06.07.2021 15:52, Eduardo Habkost wrote:
>> >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?
>>
>> Yes, the global option is unnecessary and this patch was dropped in v2.
>
>Was the behaviour this patch originally tried to fix changed in v2 as
>well? Is it going to be possible to resume a HLE=1,RTM=1 VM on a
>TSX_FORCE_ABORT=1 host with no extra kernel command line options
>needed?

The problem it tried to solve is still present, but the global switch
was thought to be unnecessary. I see that Paolo has some suggestions to
fix this in the userspace.

Thanks,
Pawan