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Date:   Tue, 6 Jul 2021 15:52:33 -0400
From:   Eduardo Habkost <ehabkost@redhat.com>
To:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
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        "H. Peter Anvin" <hpa@zytor.com>,
        "Paul E. McKenney" <paulmck@kernel.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: <20210706195233.h6w4cm73oktfqpgz@habkost.net>
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 <de6b97a567e273adff1f5268998692bad548aa10.1623272033.git-series.pawan.kumar.gupta@linux.intel.com>
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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@intel.com>
> Suggested-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
[...]

-- 
Eduardo