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Commit a6673429 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks 



While perfmon2 is a sufficiently evil library (it pokes MSRs
directly) that breaking it is fair game, it's still useful, so we
might as well try to support it.  This allows users to write 2 to
/sys/devices/cpu/rdpmc to disable all rdpmc protection so that hack
like perfmon2 can continue to work.

At some point, if perf_event becomes fast enough to replace
perfmon2, then this can go.

Signed-off-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Vince Weaver <vince@deater.net>
Cc: "hillf.zj" <hillf.zj@alibaba-inc.com>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/caac3c1c707dcca48ecbc35f4def21495856f479.1414190806.git.luto@amacapital.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 7911d3f7

arch/x86/include/asm/mmu_context.h

+4 −1
Original line number Diff line number Diff line
@@ -19,9 +19,12 @@ static inline void paravirt_activate_mm(struct mm_struct *prev, 
#endif	/* !CONFIG_PARAVIRT */



#ifdef CONFIG_PERF_EVENTS

extern struct static_key rdpmc_always_available;



static inline void load_mm_cr4(struct mm_struct *mm)

{

	if (atomic_read(&mm->context.perf_rdpmc_allowed))

	if (static_key_true(&rdpmc_always_available) ||

	    atomic_read(&mm->context.perf_rdpmc_allowed))

		cr4_set_bits(X86_CR4_PCE);

	else

		cr4_clear_bits(X86_CR4_PCE);

arch/x86/kernel/cpu/perf_event.c

+20 −1
Original line number Diff line number Diff line
@@ -45,6 +45,8 @@ DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = { 
	.enabled = 1,

};



struct static_key rdpmc_always_available = STATIC_KEY_INIT_FALSE;



u64 __read_mostly hw_cache_event_ids

				[PERF_COUNT_HW_CACHE_MAX]

				[PERF_COUNT_HW_CACHE_OP_MAX]
@@ -1870,10 +1872,27 @@ static ssize_t set_attr_rdpmc(struct device *cdev, 
	if (ret)

		return ret;



	if (val > 2)

		return -EINVAL;



	if (x86_pmu.attr_rdpmc_broken)

		return -ENOTSUPP;



	x86_pmu.attr_rdpmc = !!val;

	if ((val == 2) != (x86_pmu.attr_rdpmc == 2)) {

		/*

		 * Changing into or out of always available, aka

		 * perf-event-bypassing mode.  This path is extremely slow,

		 * but only root can trigger it, so it's okay.

		 */

		if (val == 2)

			static_key_slow_inc(&rdpmc_always_available);

		else

			static_key_slow_dec(&rdpmc_always_available);

		on_each_cpu(refresh_pce, NULL, 1);

	}



	x86_pmu.attr_rdpmc = val;



	return count;

}