linux-kernel - RE: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F077536C3CCB@SHSMSX103.ccr.corp.intel.com>
Date:   Fri, 24 Mar 2017 14:15:16 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: RE: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI



> On Thu, 23 Mar 2017, Peter Zijlstra wrote:
> > On Thu, Mar 23, 2017 at 11:25:49AM -0700, kan.liang@...el.com wrote:
> > > +	for_each_possible_cpu(cpu) {
> > > +		rdmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> &debugctlmsr);
> > > +		if (val)
> > > +			wrmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> debugctlmsr | DEBUGCTLMSR_FREEZE_WHILE_SMM);
> > > +		else
> > > +			wrmsrl_on_cpu(cpu, MSR_IA32_DEBUGCTLMSR,
> debugctlmsr & ~DEBUGCTLMSR_FREEZE_WHILE_SMM);
> > > +	}
> >
> > No; that's just disgusting. Also {rd,wr}msr_on_cpu() should die,
> > exactly because people end up writing crap like this.
> 
> Aside of that this is completely broken against other users of
> DEBUGCTLMSR because it's not atomic vs. the other modifications.
> 

OK. I will change it.
I guess I need a way/function which can atomically rd,wr msr on all cpus.
Are there existing alternative ways/functions to do that?

Thanks,
Kan