linux-kernel - RE: [PATCH V4 1/2] perf ignore LBR and extra

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077014D2005@SHSMSX103.ccr.corp.intel.com>
Date:	Wed, 9 Jul 2014 14:32:28 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH V4 1/2] perf ignore LBR and extra_regs.



> On Tue, Jul 08, 2014 at 09:49:40AM -0700, kan.liang@...el.com wrote:
> > +/*
> > + * Under certain circumstances, access certain MSR may cause #GP.
> > + * The function tests if the input MSR can be safely accessed.
> > + */
> > +static inline bool check_msr(unsigned long msr) {
> > +	u64 value;
> > +
> > +	if (rdmsrl_safe(msr, &value) < 0)
> > +		return false;
> > +	if (wrmsrl_safe(msr, value) < 0)
> > +		return false;
> > +	return true;
> > +}
> 
> What does this thing return after patch 2? does the write still fault or will
> KVM silently take writes too?

If applying patch 2, the function will return true. The KVM just simply ignore the reads/writes.
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