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Date:   Thu, 6 Oct 2022 10:35:36 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc:     Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Ricardo Neri <ricardo.neri@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Len Brown <len.brown@intel.com>, Mel Gorman <mgorman@suse.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Valentin Schneider <vschneid@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, "Tim C . Chen" <tim.c.chen@intel.com>
Subject: Re: [RFC PATCH 23/23] x86/process: Reset hardware history in context
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References: <20220909231205.14009-1-ricardo.neri-calderon@linux.intel.com>
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On Mon, Oct 03, 2022 at 04:07:58PM -0700, Ricardo Neri wrote:
> On Tue, Sep 27, 2022 at 02:52:24PM +0200, Peter Zijlstra wrote:
> > On Fri, Sep 09, 2022 at 04:12:05PM -0700, Ricardo Neri wrote:
> > 
> > > +void reset_hardware_history(void)
> > > +{
> > > +	if (!static_cpu_has(X86_FEATURE_HRESET))
> > > +		return;
> 
> If I used cpu_feature_enabled(X86_FEATURE_ITD) along with the CONFIG_HFI_
> THERMAL and its corresponding DISABLE_MASK bit the code below would be
> compiled out.

Nobody cares about compiled out -- distro's must enable all this. So
what counts is the code size, and the alternative is smaller.

> > > +
> > > +	asm volatile("mov %0, %%eax;" __ASM_HRESET "\n" : :
> > > +		     "r" (hardware_history_features) : "%rax");
> > > +}
> > 
> > 	asm_inline volatile (ALTERNATIVE("", __ASM_HRESET, X86_FEATURE_HRESET)
> > 			     : : "a" (hardware_history_features) : "memory");
> 
> Do you still prefer have implemented as an ALTERNATIVE?

Yes, look at the generated code.