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: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	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>,
	Vlastimil Babka <vbabka@suse.cz>, Tony Luck <tony.luck@intel.com>,
	Sean Christopherson <seanjc@google.com>,
	Kyung Min Park <kyung.min.park@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Juergen Gross <jgross@suse.com>,
	Krish Sadhukhan <krish.sadhukhan@oracle.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Joerg Roedel <jroedel@suse.de>,
	Victor Ding <victording@google.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Mike Rapoport <rppt@kernel.org>,
	Anthony Steinhauser <asteinhauser@google.com>,
	Anand K Mistry <amistry@google.com>,
	Andi Kleen <ak@linux.intel.com>, Miguel Ojeda <ojeda@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Joe Perches <joe@perches.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-perf-users@vger.kernel.org, kvm@vger.kernel.org,
	Jiri Denemark <jdenemar@redhat.com>,
	"libvir-list@redhat.com" <libvir-list@redhat.com>,
	Michal Privoznik <mprivozn@redhat.com>
Subject: Re: [PATCH 4/4] x86/tsx: Add cmdline tsx=fake to not clear CPUID bits RTM and HLE
Date: Wed, 7 Jul 2021 13:08:26 -0400	[thread overview]
Message-ID: <CAOpTY_pefOmJ0zJjUzitgTGxqgX6XxwTP0fMKoiyuBCHrh+AWg@mail.gmail.com> (raw)
In-Reply-To: <CALMp9eSJyvU1=FndZyR+hZMtKPWwgibKisBqp0Xcx4jxjrWn2w@mail.gmail.com>

On Wed, Jul 7, 2021 at 12:42 PM Jim Mattson <jmattson@google.com> wrote:
>
> On Wed, Jul 7, 2021 at 8:09 AM Eduardo Habkost <ehabkost@redhat.com> wrote:
> >
> > CCing libvir-list, Jiri Denemark, Michal Privoznik, so they are aware
> > that the definition of "supported CPU features" will probably become a
> > bit more complex in the future.
>
> Has there ever been a clear definition? Family, model, and stepping,
> for instance: are these the only values supported? That would make
> cross-platform migration impossible. What about the vendor string? Is
> that the only value supported? That would make cross-vendor migration
> impossible. For the maximum input value for basic CPUID information
> (CPUID.0H:EAX), is that the only value supported, or is it the maximum
> value supported? On the various individual feature bits, does a '1'
> imply that '0' is also supported, or is '1' the only value supported?
> What about the feature bits with reversed polarity (e.g.
> CPUID.(EAX=07H,ECX=0):EBX.FDP_EXCPTN_ONLY[bit 6])?
>
> This API has never made sense to me. I have no idea how to interpret
> what it is telling me.

Is this about GET_SUPPORTED_CPUID, QEMU's query-cpu-model-expansion &
related commands, or the libvirt CPU APIs?

-- 
Eduardo