From 405b45376de90b3027aaf8c4de035c6bb721fa7e Mon Sep 17 00:00:00 2001 From: Anthony Steinhauser Date: Sun, 24 Nov 2019 21:48:38 -0800 Subject: perf/x86: Implement immediate enforcement of /sys/devices/cpu/rdpmc value of 0 When you successfully write 0 to /sys/devices/cpu/rdpmc, the RDPMC instruction should be disabled unconditionally and immediately (after you close the SYSFS file) by the documentation. Instead, in the current implementation the PMU must be reloaded which happens only eventually some time in the future. Only after that the RDPMC instruction becomes disabled (on ring 3) on the respective core. This change makes the treatment of the 0 value as blocking and as unconditional as the current treatment of the 2 value, only the CR4.PCE bit is naturally set to false instead of true. Signed-off-by: Anthony Steinhauser Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Mark Rutland Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: acme@kernel.org Link: https://lkml.kernel.org/r/20191125054838.137615-1-asteinhauser@google.com Signed-off-by: Ingo Molnar --- arch/x86/events/core.c | 18 ++++++++++++------ arch/x86/include/asm/mmu_context.h | 4 +++- 2 files changed, 15 insertions(+), 7 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 6e3f0c18908e..9a89d98c55bd 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -49,6 +49,7 @@ DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = { .enabled = 1, }; +DEFINE_STATIC_KEY_FALSE(rdpmc_never_available_key); DEFINE_STATIC_KEY_FALSE(rdpmc_always_available_key); u64 __read_mostly hw_cache_event_ids @@ -2181,21 +2182,26 @@ static ssize_t set_attr_rdpmc(struct device *cdev, if (x86_pmu.attr_rdpmc_broken) return -ENOTSUPP; - if ((val == 2) != (x86_pmu.attr_rdpmc == 2)) { + if (val != x86_pmu.attr_rdpmc) { /* - * Changing into or out of always available, aka - * perf-event-bypassing mode. This path is extremely slow, + * Changing into or out of never available or always available, + * aka perf-event-bypassing mode. This path is extremely slow, * but only root can trigger it, so it's okay. */ + if (val == 0) + static_branch_inc(&rdpmc_never_available_key); + else if (x86_pmu.attr_rdpmc == 0) + static_branch_dec(&rdpmc_never_available_key); + if (val == 2) static_branch_inc(&rdpmc_always_available_key); - else + else if (x86_pmu.attr_rdpmc == 2) static_branch_dec(&rdpmc_always_available_key); + on_each_cpu(refresh_pce, NULL, 1); + x86_pmu.attr_rdpmc = val; } - x86_pmu.attr_rdpmc = val; - return count; } diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 16ae821483c8..5f33924e200f 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -26,12 +26,14 @@ static inline void paravirt_activate_mm(struct mm_struct *prev, #ifdef CONFIG_PERF_EVENTS +DECLARE_STATIC_KEY_FALSE(rdpmc_never_available_key); DECLARE_STATIC_KEY_FALSE(rdpmc_always_available_key); static inline void load_mm_cr4_irqsoff(struct mm_struct *mm) { if (static_branch_unlikely(&rdpmc_always_available_key) || - atomic_read(&mm->context.perf_rdpmc_allowed)) + (!static_branch_unlikely(&rdpmc_never_available_key) && + atomic_read(&mm->context.perf_rdpmc_allowed))) cr4_set_bits_irqsoff(X86_CR4_PCE); else cr4_clear_bits_irqsoff(X86_CR4_PCE); -- cgit