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SubjectRE: [PATCH v2 7/8] x86, perf: Only allow rdpmc if a perf_event is mapped
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> >> Subject: Re: [PATCH v2 7/8] x86, perf: Only allow rdpmc if a perf_event is mapped
> >>
> > CPU D CPU A
> > switch_mm
> > load_mm_cr4
> > x86_pmu_event_unmapped
> >
> > I wonder if the X86_CR4_PCE set on CPU D is
> > cleared by CPU A by broadcasting IPI.
> >
>
> It should be okay. The IPI does:
>
> + if (current->mm)
> + load_mm_cr4(current->mm);
>
> which refers to the current task running on the targetted CPU, not to
> the IPI sender's task. So, if it happens after a context switch, it
> will harmlessly reload the new task's cr4.
>
Right, but prev != next is checked in switch_mm.

Hillf




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