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

From: Eduardo Habkost <ehabkost@redhat.com>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>, Jonathan Corbet <corbet@lwn.net>,
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	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>,
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	linux-perf-users@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE
Date: Tue, 6 Jul 2021 17:19:42 -0400	[thread overview]
Message-ID: <CAOpTY_pmNah_OCzk3XRyTsgkCPdJD1tp2RxKHMieFQM1s-tQNA@mail.gmail.com> (raw)
In-Reply-To: <20210706211606.ezme3xvwztagbjqy@gupta-dev2.localdomain>

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?

-- 
Eduardo