From 83a7a4d643d33a8b74a42229346b7ed7139fcef9 Mon Sep 17 00:00:00 2001 From: Rob Herring Date: Wed, 8 Dec 2021 14:11:23 -0600 Subject: [PATCH] arm64: perf: Enable PMU counter userspace access for perf event Arm PMUs can support direct userspace access of counters which allows for low overhead (i.e. no syscall) self-monitoring of tasks. The same feature exists on x86 called 'rdpmc'. Unlike x86, userspace access will only be enabled for thread bound events. This could be extended if needed, but simplifies the implementation and reduces the chances for any information leaks (which the x86 implementation suffers from). PMU EL0 access will be enabled when an event with userspace access is part of the thread's context. This includes when the event is not scheduled on the PMU. There's some additional overhead clearing dirty counters when access is enabled in order to prevent leaking disabled counter data from other tasks. Unlike x86, enabling of userspace access must be requested with a new attr bit: config1:1. If the user requests userspace access with 64-bit counters, then the event open will fail if the h/w doesn't support 64-bit counters. Chaining is not supported with userspace access. The modes for config1 are as follows: config1 = 0 : user access disabled and always 32-bit config1 = 1 : user access disabled and always 64-bit (using chaining if needed) config1 = 2 : user access enabled and always 32-bit config1 = 3 : user access enabled and always 64-bit Based on work by Raphael Gault , but has been completely re-written. Cc: Will Deacon Cc: Mark Rutland Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Namhyung Kim Cc: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org Cc: linux-perf-users@vger.kernel.org Signed-off-by: Rob Herring Link: https://lore.kernel.org/r/20211208201124.310740-5-robh@kernel.org [will: Made armv8pmu_proc_user_access_handler() static] Signed-off-by: Will Deacon --- arch/arm64/kernel/perf_event.c | 119 +++++++++++++++++++++++++++++++-- 1 file changed, 112 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c index 6ae20c4217af69..81cc9f0e718aba 100644 --- a/arch/arm64/kernel/perf_event.c +++ b/arch/arm64/kernel/perf_event.c @@ -285,6 +285,7 @@ static const struct attribute_group armv8_pmuv3_events_attr_group = { PMU_FORMAT_ATTR(event, "config:0-15"); PMU_FORMAT_ATTR(long, "config1:0"); +PMU_FORMAT_ATTR(rdpmc, "config1:1"); static int sysctl_perf_user_access __read_mostly; @@ -293,9 +294,15 @@ static inline bool armv8pmu_event_is_64bit(struct perf_event *event) return event->attr.config1 & 0x1; } +static inline bool armv8pmu_event_want_user_access(struct perf_event *event) +{ + return event->attr.config1 & 0x2; +} + static struct attribute *armv8_pmuv3_format_attrs[] = { &format_attr_event.attr, &format_attr_long.attr, + &format_attr_rdpmc.attr, NULL, }; @@ -364,7 +371,7 @@ static const struct attribute_group armv8_pmuv3_caps_attr_group = { */ #define ARMV8_IDX_CYCLE_COUNTER 0 #define ARMV8_IDX_COUNTER0 1 - +#define ARMV8_IDX_CYCLE_COUNTER_USER 32 /* * We unconditionally enable ARMv8.5-PMU long event counter support @@ -376,18 +383,22 @@ static bool armv8pmu_has_long_event(struct arm_pmu *cpu_pmu) return (cpu_pmu->pmuver >= ID_AA64DFR0_PMUVER_8_5); } +static inline bool armv8pmu_event_has_user_read(struct perf_event *event) +{ + return event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT; +} + /* * We must chain two programmable counters for 64 bit events, * except when we have allocated the 64bit cycle counter (for CPU - * cycles event). This must be called only when the event has - * a counter allocated. + * cycles event) or when user space counter access is enabled. */ static inline bool armv8pmu_event_is_chained(struct perf_event *event) { int idx = event->hw.idx; struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu); - return !WARN_ON(idx < 0) && + return !armv8pmu_event_has_user_read(event) && armv8pmu_event_is_64bit(event) && !armv8pmu_has_long_event(cpu_pmu) && (idx != ARMV8_IDX_CYCLE_COUNTER); @@ -720,6 +731,28 @@ static inline u32 armv8pmu_getreset_flags(void) return value; } +static void armv8pmu_disable_user_access(void) +{ + write_sysreg(0, pmuserenr_el0); +} + +static void armv8pmu_enable_user_access(struct arm_pmu *cpu_pmu) +{ + int i; + struct pmu_hw_events *cpuc = this_cpu_ptr(cpu_pmu->hw_events); + + /* Clear any unused counters to avoid leaking their contents */ + for_each_clear_bit(i, cpuc->used_mask, cpu_pmu->num_events) { + if (i == ARMV8_IDX_CYCLE_COUNTER) + write_sysreg(0, pmccntr_el0); + else + armv8pmu_write_evcntr(i, 0); + } + + write_sysreg(0, pmuserenr_el0); + write_sysreg(ARMV8_PMU_USERENR_ER | ARMV8_PMU_USERENR_CR, pmuserenr_el0); +} + static void armv8pmu_enable_event(struct perf_event *event) { /* @@ -763,6 +796,14 @@ static void armv8pmu_disable_event(struct perf_event *event) static void armv8pmu_start(struct arm_pmu *cpu_pmu) { + struct perf_event_context *task_ctx = + this_cpu_ptr(cpu_pmu->pmu.pmu_cpu_context)->task_ctx; + + if (sysctl_perf_user_access && task_ctx && task_ctx->nr_user) + armv8pmu_enable_user_access(cpu_pmu); + else + armv8pmu_disable_user_access(); + /* Enable all counters */ armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E); } @@ -880,13 +921,16 @@ static int armv8pmu_get_event_idx(struct pmu_hw_events *cpuc, if (evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) { if (!test_and_set_bit(ARMV8_IDX_CYCLE_COUNTER, cpuc->used_mask)) return ARMV8_IDX_CYCLE_COUNTER; + else if (armv8pmu_event_is_64bit(event) && + armv8pmu_event_want_user_access(event) && + !armv8pmu_has_long_event(cpu_pmu)) + return -EAGAIN; } /* * Otherwise use events counters */ - if (armv8pmu_event_is_64bit(event) && - !armv8pmu_has_long_event(cpu_pmu)) + if (armv8pmu_event_is_chained(event)) return armv8pmu_get_chain_idx(cpuc, cpu_pmu); else return armv8pmu_get_single_idx(cpuc, cpu_pmu); @@ -902,6 +946,22 @@ static void armv8pmu_clear_event_idx(struct pmu_hw_events *cpuc, clear_bit(idx - 1, cpuc->used_mask); } +static int armv8pmu_user_event_idx(struct perf_event *event) +{ + if (!sysctl_perf_user_access || !armv8pmu_event_has_user_read(event)) + return 0; + + /* + * We remap the cycle counter index to 32 to + * match the offset applied to the rest of + * the counter indices. + */ + if (event->hw.idx == ARMV8_IDX_CYCLE_COUNTER) + return ARMV8_IDX_CYCLE_COUNTER_USER; + + return event->hw.idx; +} + /* * Add an event filter to a given event. */ @@ -998,6 +1058,25 @@ static int __armv8_pmuv3_map_event(struct perf_event *event, if (armv8pmu_event_is_64bit(event)) event->hw.flags |= ARMPMU_EVT_64BIT; + /* + * User events must be allocated into a single counter, and so + * must not be chained. + * + * Most 64-bit events require long counter support, but 64-bit + * CPU_CYCLES events can be placed into the dedicated cycle + * counter when this is free. + */ + if (armv8pmu_event_want_user_access(event)) { + if (!(event->attach_state & PERF_ATTACH_TASK)) + return -EINVAL; + if (armv8pmu_event_is_64bit(event) && + (hw_event_id != ARMV8_PMUV3_PERFCTR_CPU_CYCLES) && + !armv8pmu_has_long_event(armpmu)) + return -EOPNOTSUPP; + + event->hw.flags |= PERF_EVENT_FLAG_USER_READ_CNT; + } + /* Only expose micro/arch events supported by this PMU */ if ((hw_event_id > 0) && (hw_event_id < ARMV8_PMUV3_MAX_COMMON_EVENTS) && test_bit(hw_event_id, armpmu->pmceid_bitmap)) { @@ -1106,13 +1185,29 @@ static int armv8pmu_probe_pmu(struct arm_pmu *cpu_pmu) return probe.present ? 0 : -ENODEV; } +static void armv8pmu_disable_user_access_ipi(void *unused) +{ + armv8pmu_disable_user_access(); +} + +static int armv8pmu_proc_user_access_handler(struct ctl_table *table, int write, + void *buffer, size_t *lenp, loff_t *ppos) +{ + int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + if (ret || !write || sysctl_perf_user_access) + return ret; + + on_each_cpu(armv8pmu_disable_user_access_ipi, NULL, 1); + return 0; +} + static struct ctl_table armv8_pmu_sysctl_table[] = { { .procname = "perf_user_access", .data = &sysctl_perf_user_access, .maxlen = sizeof(unsigned int), .mode = 0644, - .proc_handler = proc_dointvec_minmax, + .proc_handler = armv8pmu_proc_user_access_handler, .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_ONE, }, @@ -1142,6 +1237,8 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, cpu_pmu->set_event_filter = armv8pmu_set_event_filter; cpu_pmu->filter_match = armv8pmu_filter_match; + cpu_pmu->pmu.event_idx = armv8pmu_user_event_idx; + cpu_pmu->name = name; cpu_pmu->map_event = map_event; cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_EVENTS] = events ? @@ -1318,6 +1415,14 @@ void arch_perf_update_userpage(struct perf_event *event, userpg->cap_user_time = 0; userpg->cap_user_time_zero = 0; userpg->cap_user_time_short = 0; + userpg->cap_user_rdpmc = armv8pmu_event_has_user_read(event); + + if (userpg->cap_user_rdpmc) { + if (event->hw.flags & ARMPMU_EVT_64BIT) + userpg->pmc_width = 64; + else + userpg->pmc_width = 32; + } do { rd = sched_clock_read_begin(&seq);