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Message-ID: <20151204115335.GB15308@gmail.com>
Date: Fri, 4 Dec 2015 12:53:35 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Amy Wiles <amy.l.wiles@...el.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
LKML <linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/rapl: Do not load in a guest
* Borislav Petkov <bp@...en8.de> wrote:
> On Fri, Dec 04, 2015 at 11:41:03AM +0100, Paolo Bonzini wrote:
> > No, please don't. Why do you need a wrmsr instead of a rdmsr? If
> > there's no RAPL domains, the device doesn't load. On hypervisors,
> > reading random MSRs is generally safe.
>
> Well, we could not do anything, sure, that's an option too. It would
> only be the annoying error message. Which is
>
> pr_err("no valid rapl domains found in package %d\n", rp->id);
>
> I guess we can tone that down as apparently it is not an error to
> not have valid rapl domains anymore. Maybe kill it altogether:
> rapl_detect_topology() will propagate the error and the driver won't
> load...
So given than nothing really tells us in a clear way whether RAPL is supported or
not on that kernel, it might be better to just centralize the 'detect RAPL'
function, and print "x86/rapl: Feature detected" on bootup. That function can also
install a synthetic CPUID bit, which all other code could use in a clean fashion.
Since it will be an __init function, there's not much of an overhead argument
against it.
This way it becomes part of the CPUID infrastructure - and eventually it might
even grow a real CPUID bit in future CPU models.
and we'll have a lot less RAPL detection muck all around. Win-win.
Thanks,
Ingo
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