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SubjectRe: [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@intel.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.

Thanks,

tglx





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