On Mon, Oct 27, 2014 at 8:35 PM, Hillf Danton <hillf...@alibaba-inc.com> wrote: >> -----Original Message----- >> From: Andy Lutomirski [mailto:l...@amacapital.net] >> Sent: Monday, October 27, 2014 11:45 PM >> To: Hillf Danton >> Cc: Peter Zijlstra; Ingo Molnar; Vince Weaver; Paul Mackerras; Kees Cook; >> Arnaldo Carvalho de Melo; Andrea Arcangeli; linux- >> ker...@vger.kernel.org; Valdis Kletnieks >> 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. refresh_pce can't happen in between switch_mm and updating current, since irqs are off for the entire duration of the context switch. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
