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perf/x86: Add /sys/devices/cpu/rdpmc=2 to allow rdpmc for all tasks

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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: Andy Lutomirski <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: "hillf.zj" <[email protected]>
Cc: Valdis Kletnieks <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/caac3c1c707dcca48ecbc35f4def21495856f479.1414190806.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Andy Lutomirski authored and Ingo Molnar committed 2015-02-04 12:10:49 +01:00
1 parent 7911d3f7af
commit a66734297f
2 files changed
+24 -2
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arch/x86/include/asm/mmu_context.h
+4 -1
View File
@@ -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
View File
@@ -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;
}