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 <l...@amacapital.net>
---
arch/x86/include/asm/mmu_context.h | 5 ++++-
arch/x86/kernel/cpu/perf_event.c | 21 ++++++++++++++++++++-
2 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/mmu_context.h
b/arch/x86/include/asm/mmu_context.h
index ccad8d616038..6133f0d02ea4 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -20,9 +20,12 @@ 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);
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 3e875b3b30f2..31fc31e0cf9b 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -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]
@@ -1878,10 +1880,27 @@ 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;
}
--
1.9.3
--
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