[PATCH v1 34/41] perf pmu: Probe user and interrupt sample register masks

[Ian Rogers]

Extend perf_pmu__probe() with probe_pmu_regs_one() to probe supported
register sampling masks for PERF_SAMPLE_REGS_USER and
PERF_SAMPLE_REGS_INTR when supported by the PMU.

Test the architecture's base general-purpose register mask as a batch
before falling back to per-register probing if needed, and on hardware
PMUs also probe extended GPRs (such as x86 APX R16-R31 and CET SSP) and
SIMD vector/predicate register classes via PERF_SAMPLE_REGS_ABI_SIMD.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/pmu.c | 249 ++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/pmu.h |  28 +++++
 2 files changed, 277 insertions(+)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 3585147c5242..9179231aa7d5 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -3386,6 +3386,237 @@ static void probe_sample_types(struct perf_pmu *pmu,
 	pmu->probed.can_weight = !!(pmu->probed.sample_types & PERF_SAMPLE_WEIGHT);
 }
 
+/*
+ * Probe supported general-purpose, extended GPR, and SIMD vector/predicate
+ * register sampling masks for either PERF_SAMPLE_REGS_USER (!@intr) or
+ * PERF_SAMPLE_REGS_INTR (@intr).
+ */
+static void probe_pmu_regs_one(const struct perf_pmu *pmu,
+			       const struct perf_event_attr *base_attr,
+			       pid_t pid, int cpu, unsigned long flags,
+			       int max_precise, bool intr,
+			       u64 *out_mask, int *out_abi,
+			       u64 *out_simd_mask, u64 *out_pred_mask)
+{
+	int dummy_abi = -1;
+	u64 gpr_mask = intr ? perf_intr_reg_mask(EM_HOST, &dummy_abi) :
+			      perf_user_reg_mask(EM_HOST, &dummy_abi);
+	u64 sample_type = intr ? PERF_SAMPLE_REGS_INTR : PERF_SAMPLE_REGS_USER;
+	u64 mask = 0;
+	int abi = 0;
+	struct perf_event_attr attr = *base_attr;
+	int fd;
+
+	attr.disabled = 1;
+	attr.sample_period = base_attr->sample_period ?: 10000;
+	attr.sample_type = sample_type;
+
+	if (gpr_mask) {
+		if (intr)
+			attr.sample_regs_intr = gpr_mask;
+		else
+			attr.sample_regs_user = gpr_mask;
+
+		fd = sys_perf_event_open(&attr, pid, cpu, -1, flags);
+		if (fd >= 0) {
+			close(fd);
+			mask |= gpr_mask;
+		} else {
+			for (int b = 0; b < 64; b++) {
+				if (!(gpr_mask & BIT_ULL(b)))
+					continue;
+				if (intr)
+					attr.sample_regs_intr = BIT_ULL(b);
+				else
+					attr.sample_regs_user = BIT_ULL(b);
+				fd = sys_perf_event_open(&attr, pid, cpu, -1, flags);
+				if (fd >= 0) {
+					close(fd);
+					mask |= BIT_ULL(b);
+				}
+			}
+		}
+	}
+
+	if (perf_pmu__is_software(pmu)) {
+		*out_mask = mask;
+		*out_abi = abi;
+		return;
+	}
+
+	/*
+	 * Probe extended GPRs outside the base GPR mask when the host ABI
+	 * supports PERF_SAMPLE_REGS_ABI_SIMD (e.g. APX R16-R31 and CET SSP).
+	 * Note: perf_pmu__probe() actively probes the running host kernel via
+	 * perf_event_open(), so EM_HOST is used intentionally here.
+	 */
+	{
+		int host_abi = 0;
+		u64 host_mask = intr ? perf_intr_reg_mask(EM_HOST, &host_abi) :
+				       perf_user_reg_mask(EM_HOST, &host_abi);
+		u64 ext_gpr_mask = host_mask & ~gpr_mask;
+
+		if ((host_abi & PERF_SAMPLE_REGS_ABI_SIMD) && ext_gpr_mask) {
+			struct perf_event_attr e_attr = *base_attr;
+			bool ext_batch_ok = false;
+
+			e_attr.size = sizeof(e_attr);
+			e_attr.disabled = 1;
+			e_attr.sample_period = base_attr->sample_period ?: 10000;
+			e_attr.sample_type = sample_type;
+			e_attr.sample_simd_regs_enabled = 1;
+			if (intr)
+				e_attr.sample_regs_intr = ext_gpr_mask;
+			else
+				e_attr.sample_regs_user = ext_gpr_mask;
+
+			fd = sys_perf_event_open(&e_attr, pid, cpu, -1, flags);
+			if (fd < 0 && intr && max_precise > 0) {
+				e_attr.precise_ip = 1;
+				fd = sys_perf_event_open(&e_attr, pid, cpu, -1, flags);
+			}
+			if (fd >= 0) {
+				close(fd);
+				mask |= ext_gpr_mask;
+				abi |= PERF_SAMPLE_REGS_ABI_SIMD;
+				ext_batch_ok = true;
+			}
+
+			if (!ext_batch_ok) {
+				for (int b = 0; b < 64; b++) {
+					if (!(ext_gpr_mask & BIT_ULL(b)))
+						continue;
+					e_attr.precise_ip = base_attr->precise_ip;
+					if (intr)
+						e_attr.sample_regs_intr = BIT_ULL(b);
+					else
+						e_attr.sample_regs_user = BIT_ULL(b);
+					fd = sys_perf_event_open(&e_attr, pid, cpu, -1, flags);
+					if (fd < 0 && intr && max_precise > 0) {
+						e_attr.precise_ip = 1;
+						fd = sys_perf_event_open(&e_attr, pid, cpu, -1,
+									 flags);
+					}
+					if (fd >= 0) {
+						close(fd);
+						mask |= BIT_ULL(b);
+						abi |= PERF_SAMPLE_REGS_ABI_SIMD;
+					}
+				}
+			}
+		}
+	}
+
+	for (int is_pred = 0; is_pred <= 1; is_pred++) {
+		bool pred = is_pred != 0;
+		u64 class_mask = intr ?
+			perf_intr_simd_reg_class_mask(EM_HOST, pred) :
+			perf_user_simd_reg_class_mask(EM_HOST, pred);
+		u64 supported_classes = 0;
+
+		for (int reg_c = 0; reg_c < 64; reg_c++) {
+			struct perf_event_attr s_attr = *base_attr;
+			u16 qwords = 0;
+			u64 bitmap;
+
+			if (!(class_mask & BIT_ULL(reg_c)))
+				continue;
+			bitmap = intr ?
+				perf_intr_simd_reg_class_bitmap_qwords(EM_HOST, reg_c,
+								       &qwords, pred) :
+				perf_user_simd_reg_class_bitmap_qwords(EM_HOST, reg_c,
+								       &qwords, pred);
+			if (!bitmap || !qwords)
+				continue;
+
+			s_attr.size = sizeof(s_attr);
+			s_attr.disabled = 1;
+			s_attr.sample_period = base_attr->sample_period ?: 10000;
+			s_attr.sample_type = sample_type;
+			s_attr.sample_simd_regs_enabled = 1;
+			if (pred) {
+				s_attr.sample_simd_pred_reg_qwords = qwords;
+				if (intr)
+					s_attr.sample_simd_pred_reg_intr = bitmap;
+				else
+					s_attr.sample_simd_pred_reg_user = bitmap;
+			} else {
+				s_attr.sample_simd_vec_reg_qwords = qwords;
+				if (intr)
+					s_attr.sample_simd_vec_reg_intr = bitmap;
+				else
+					s_attr.sample_simd_vec_reg_user = bitmap;
+			}
+
+			fd = sys_perf_event_open(&s_attr, pid, cpu, -1, flags);
+			if (fd < 0 && intr && max_precise > 0) {
+				s_attr.precise_ip = 1;
+				fd = sys_perf_event_open(&s_attr, pid, cpu, -1, flags);
+			}
+			if (fd >= 0) {
+				close(fd);
+				supported_classes |= BIT_ULL(reg_c);
+				abi |= PERF_SAMPLE_REGS_ABI_SIMD;
+			}
+		}
+
+		if (pred)
+			*out_pred_mask = supported_classes;
+		else
+			*out_simd_mask = supported_classes;
+	}
+
+	if (!(abi & PERF_SAMPLE_REGS_ABI_SIMD)) {
+		u64 ext_mask = GENMASK_ULL(63, 32) & ~gpr_mask;
+		struct perf_event_attr x_attr = *base_attr;
+		bool batch_ok = false;
+
+		x_attr.disabled = 1;
+		x_attr.sample_period = base_attr->sample_period ?: 10000;
+		x_attr.sample_type = sample_type;
+		if (intr && max_precise > 0)
+			x_attr.precise_ip = 1;
+
+		if (ext_mask) {
+			if (intr)
+				x_attr.sample_regs_intr = ext_mask;
+			else
+				x_attr.sample_regs_user = ext_mask;
+
+			fd = sys_perf_event_open(&x_attr, pid, cpu, -1, flags);
+			if (fd >= 0) {
+				close(fd);
+				mask |= ext_mask;
+				batch_ok = true;
+			}
+		}
+
+		if (!batch_ok) {
+			for (int b = 0; b < 64; b++) {
+				const char *rname;
+
+				if (gpr_mask & BIT_ULL(b))
+					continue;
+				rname = perf_reg_name(b, EM_HOST, EF_HOST, 0);
+				if (!rname || !strcmp(rname, "unknown"))
+					continue;
+				if (intr)
+					x_attr.sample_regs_intr = BIT_ULL(b);
+				else
+					x_attr.sample_regs_user = BIT_ULL(b);
+				fd = sys_perf_event_open(&x_attr, pid, cpu, -1, flags);
+				if (fd >= 0) {
+					close(fd);
+					mask |= BIT_ULL(b);
+				}
+			}
+		}
+	}
+
+	*out_mask = mask;
+	*out_abi = abi;
+}
+
 /*
  * Pack @value into the perf_event_attr config field named by the sysfs format
  * @name of @pmu, e.g. "rdpmc" defined as "config1:1". Returns false if the
@@ -3762,6 +3993,24 @@ static void __perf_pmu__probe(struct perf_pmu *pmu, int pmu_cpu)
 		}
 	}
 
+	/* 3b. User and interrupt register sampling masks */
+	if (pmu->probed.sample_types & PERF_SAMPLE_REGS_USER) {
+		probe_pmu_regs_one(pmu, &base_attr, pid, cpu, flags,
+				   pmu->probed.max_precise, /*intr=*/false,
+				   &pmu->probed.user_regs_mask,
+				   &pmu->probed.user_regs_abi,
+				   &pmu->probed.user_simd_mask,
+				   &pmu->probed.user_pred_mask);
+	}
+	if (pmu->probed.sample_types & PERF_SAMPLE_REGS_INTR) {
+		probe_pmu_regs_one(pmu, &base_attr, pid, cpu, flags,
+				   pmu->probed.max_precise, /*intr=*/true,
+				   &pmu->probed.intr_regs_mask,
+				   &pmu->probed.intr_regs_abi,
+				   &pmu->probed.intr_simd_mask,
+				   &pmu->probed.intr_pred_mask);
+	}
+
 	/* 4. Privilege / exclusion modifiers */
 	pmu->probed.exclude_user =
 		test_exclude_flag(&base_attr, pid, cpu, flags, PROBE_EXCLUDE_USER);
diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index cacb8bc5198b..66ee3841872a 100644
--- a/tools/perf/util/pmu.h
+++ b/tools/perf/util/pmu.h
@@ -300,11 +300,39 @@ struct perf_pmu {
 		 * in a group counted simultaneously, without multiplexing.
 		 */
 		int max_gp_group_size;
+		/** @probed.user_regs_abi: ABI flags for user_regs_mask. */
+		int user_regs_abi;
+		/** @probed.intr_regs_abi: ABI flags for intr_regs_mask. */
+		int intr_regs_abi;
 		/**
 		 * @probed.sample_types: Bitmask of supported
 		 * enum perf_event_sample_format flags.
 		 */
 		u64 sample_types;
+		/** @probed.user_regs_mask: Bitmask of supported sample_regs_user registers. */
+		u64 user_regs_mask;
+		/** @probed.intr_regs_mask: Bitmask of supported sample_regs_intr registers. */
+		u64 intr_regs_mask;
+		/**
+		 * @probed.user_simd_mask: Bitmask of supported user SIMD vector
+		 * register classes.
+		 */
+		u64 user_simd_mask;
+		/**
+		 * @probed.user_pred_mask: Bitmask of supported user SIMD predicate
+		 * register classes.
+		 */
+		u64 user_pred_mask;
+		/**
+		 * @probed.intr_simd_mask: Bitmask of supported intr SIMD vector
+		 * register classes.
+		 */
+		u64 intr_simd_mask;
+		/**
+		 * @probed.intr_pred_mask: Bitmask of supported intr SIMD predicate
+		 * register classes.
+		 */
+		u64 intr_pred_mask;
 	} probed;
 };
 
-- 
2.56.0.385.gac671c819a-goog