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

[Liang, Kan]

> On Thu, 23 Mar 2017, Peter Zijlstra wrote:
> > On Thu, Mar 23, 2017 at 11:25:49AM -0700, kan.liang@xxxxxxxxx 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