[Patch v8 12/23] perf: Add sampling support for SIMD registers

[Dapeng Mi]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Users may be interested in sampling SIMD registers during profiling.
The current sample_regs_* structure does not have sufficient space
for all SIMD registers.

To address this, new attribute fields sample_simd_{pred,vec}_reg_* are
added to struct perf_event_attr to represent the SIMD registers that are
expected to be sampled.

Currently, the perf/x86 code supports XMM registers in sample_regs_*.
To unify the configuration of SIMD registers and ensure a consistent
method for configuring XMM and other SIMD registers, a new event
attribute field, sample_simd_regs_enabled, is introduced. When
sample_simd_regs_enabled is set, it indicates that all SIMD registers,
including XMM, will be represented by the newly introduced
sample_simd_{pred|vec}_reg_* fields. The original XMM space in
sample_regs_* is reserved for future uses.

Since SIMD registers are wider than 64 bits, a new output format is
introduced. The number and width of SIMD registers are dumped first,
followed by the register values. The number and width are based on the
user's configuration.

A new ABI, PERF_SAMPLE_REGS_ABI_SIMD, is added to indicate the new format.
The enum perf_sample_regs_abi is now a bitmap. This change should not
impact existing tools, as the version and bitmap remain the same for
values 1 and 2.

Additionally, two new __weak functions are introduced:
- perf_simd_reg_value(): Retrieves the value of the requested SIMD
  register.
- perf_simd_reg_validate(): Validates the configuration of the SIMD
  registers.

A new flag, PERF_PMU_CAP_SIMD_REGS, is added to indicate that the PMU
supports SIMD register dumping. An error is generated if
sample_simd_{pred|vec}_reg_* is mistakenly set for a PMU that does not
support this capability.

Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Co-developed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
---
 include/linux/perf_event.h      |   8 ++
 include/linux/perf_regs.h       |   6 ++
 include/uapi/linux/perf_event.h |  49 +++++++++-
 kernel/events/core.c            | 153 +++++++++++++++++++++++++++++---
 4 files changed, 202 insertions(+), 14 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index fb38affa7352..5f0642ef4fd2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -306,6 +306,7 @@ struct perf_event_pmu_context;
 #define PERF_PMU_CAP_AUX_PAUSE		0x0200
 #define PERF_PMU_CAP_AUX_PREFER_LARGE	0x0400
 #define PERF_PMU_CAP_MEDIATED_VPMU	0x0800
+#define PERF_PMU_CAP_SIMD_REGS		0x1000
 
 /**
  * pmu::scope
@@ -1534,6 +1535,13 @@ perf_event__output_id_sample(struct perf_event *event,
 extern void
 perf_log_lost_samples(struct perf_event *event, u64 lost);
 
+static inline bool event_has_simd_regs(struct perf_event *event)
+{
+	struct perf_event_attr *attr = &event->attr;
+
+	return attr->sample_simd_regs_enabled != 0;
+}
+
 static inline bool event_has_extended_regs(struct perf_event *event)
 {
 	struct perf_event_attr *attr = &event->attr;
diff --git a/include/linux/perf_regs.h b/include/linux/perf_regs.h
index 144bcc3ff19f..8fa3eeb14953 100644
--- a/include/linux/perf_regs.h
+++ b/include/linux/perf_regs.h
@@ -14,6 +14,12 @@ int perf_reg_validate(u64 mask);
 u64 perf_reg_abi(struct task_struct *task);
 void perf_get_regs_user(struct perf_regs *regs_user,
 			struct pt_regs *regs);
+int perf_simd_reg_validate(u16 simd_enabled, u16 vec_qwords,
+			   u64 vec_mask_intr, u64 vec_mask_user,
+			   u16 pred_qwords, u32 pred_mask_intr,
+			   u32 pred_mask_user);
+u64 perf_simd_reg_value(struct pt_regs *regs, int idx,
+			u16 qwords_idx, bool pred);
 
 #ifdef CONFIG_HAVE_PERF_REGS
 #include <asm/perf_regs.h>
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index fd10aa8d697f..c49fc76292f7 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -314,8 +314,9 @@ enum {
  */
 enum perf_sample_regs_abi {
 	PERF_SAMPLE_REGS_ABI_NONE		= 0,
-	PERF_SAMPLE_REGS_ABI_32			= 1,
-	PERF_SAMPLE_REGS_ABI_64			= 2,
+	PERF_SAMPLE_REGS_ABI_32			= (1 << 0),
+	PERF_SAMPLE_REGS_ABI_64			= (1 << 1),
+	PERF_SAMPLE_REGS_ABI_SIMD		= (1 << 2),
 };
 
 /*
@@ -383,6 +384,7 @@ enum perf_event_read_format {
 #define PERF_ATTR_SIZE_VER7			128	/* Add: sig_data */
 #define PERF_ATTR_SIZE_VER8			136	/* Add: config3 */
 #define PERF_ATTR_SIZE_VER9			144	/* add: config4 */
+#define PERF_ATTR_SIZE_VER10			176	/* Add: sample_simd_{vec|pred}_reg_* */
 
 /*
  * 'struct perf_event_attr' contains various attributes that define
@@ -547,6 +549,29 @@ struct perf_event_attr {
 
 	__u64	config3; /* extension of config2 */
 	__u64	config4; /* extension of config3 */
+
+	/*
+	 * Defines the sampling SIMD/PRED(predicate) registers bitmap and
+	 * qwords (8 bytes) length.
+	 *
+	 * sample_simd_regs_enabled != 0 indicates there are SIMD/PRED
+	 * registers to be sampled, the SIMD/PRED registers bitmap and
+	 * qwords length are represented in
+	 * sample_simd_{vec|pred}_reg_{intr|user} and
+	 * sample_simd_{vec|pred}_reg_qwords fields separately.
+	 *
+	 * sample_simd_regs_enabled == 0 indicates no SIMD/PRED registers
+	 * are sampled.
+	 */
+	__u16	sample_simd_regs_enabled;
+	__u16	sample_simd_pred_reg_qwords;
+	__u16	sample_simd_vec_reg_qwords;
+	__u16	__reserved_4;
+
+	__u32	sample_simd_pred_reg_intr;
+	__u32	sample_simd_pred_reg_user;
+	__u64	sample_simd_vec_reg_intr;
+	__u64	sample_simd_vec_reg_user;
 };
 
 /*
@@ -1020,7 +1045,15 @@ enum perf_event_type {
 	 *      } && PERF_SAMPLE_BRANCH_STACK
 	 *
 	 *	{ u64			abi; # enum perf_sample_regs_abi
-	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_USER
+	 *	  u64			regs[weight(mask)];
+	 *	  struct {
+	 *		u64 nr_vectors;		# 0 ... weight(sample_simd_vec_reg_user)
+	 *		u64 vector_qwords;	# 0 ... sample_simd_vec_reg_qwords
+	 *		u64 nr_pred;		# 0 ... weight(sample_simd_pred_reg_user)
+	 *		u64 pred_qwords;	# 0 ... sample_simd_pred_reg_qwords
+	 *		u64 data[nr_vectors * vector_qwords + nr_pred * pred_qwords];
+	 *	  } && (abi & PERF_SAMPLE_REGS_ABI_SIMD)
+	 *	} && PERF_SAMPLE_REGS_USER
 	 *
 	 *	{ u64			size;
 	 *	  char			data[size];
@@ -1047,7 +1080,15 @@ enum perf_event_type {
 	 *	{ u64			data_src; } && PERF_SAMPLE_DATA_SRC
 	 *	{ u64			transaction; } && PERF_SAMPLE_TRANSACTION
 	 *	{ u64			abi; # enum perf_sample_regs_abi
-	 *	  u64			regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
+	 *	  u64			regs[weight(mask)];
+	 *	  struct {
+	 *		u64 nr_vectors;		# 0 ... weight(sample_simd_vec_reg_intr)
+	 *		u64 vector_qwords;	# 0 ... sample_simd_vec_reg_qwords
+	 *		u64 nr_pred;		# 0 ... weight(sample_simd_pred_reg_intr)
+	 *		u64 pred_qwords;	# 0 ... sample_simd_pred_reg_qwords
+	 *		u64 data[nr_vectors * vector_qwords + nr_pred * pred_qwords];
+	 *	  } && (abi & PERF_SAMPLE_REGS_ABI_SIMD)
+	 *	} && PERF_SAMPLE_REGS_INTR
 	 *	{ u64			phys_addr;} && PERF_SAMPLE_PHYS_ADDR
 	 *	{ u64			cgroup;} && PERF_SAMPLE_CGROUP
 	 *	{ u64			data_page_size;} && PERF_SAMPLE_DATA_PAGE_SIZE
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2ce553db4dcb..94bb034da9b9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7791,22 +7791,60 @@ void __weak perf_get_regs_user(struct perf_regs *regs_user,
 	regs_user->abi = perf_reg_abi(current);
 }
 
+#define word_for_each_set_bit(bit, val)			\
+	for (unsigned long long __v = (val);		\
+	     __v && ((bit = __builtin_ctzll(__v)), 1);	\
+	     __v &= __v - 1)
+
 static void
 perf_output_sample_regs(struct perf_output_handle *handle,
 			struct pt_regs *regs, u64 mask)
 {
 	int bit;
-	DECLARE_BITMAP(_mask, 64);
-
-	bitmap_from_u64(_mask, mask);
-	for_each_set_bit(bit, _mask, sizeof(mask) * BITS_PER_BYTE) {
-		u64 val;
 
-		val = perf_reg_value(regs, bit);
+	word_for_each_set_bit(bit, mask) {
+		u64 val = perf_reg_value(regs, bit);
 		perf_output_put(handle, val);
 	}
 }
 
+static void
+perf_output_sample_simd_regs(struct perf_output_handle *handle,
+			     struct perf_event *event,
+			     struct pt_regs *regs,
+			     u64 mask, u32 pred_mask)
+{
+	u64 pred_qwords = event->attr.sample_simd_pred_reg_qwords;
+	u64 vec_qwords = event->attr.sample_simd_vec_reg_qwords;
+	u64 nr_vectors = hweight64(mask);
+	u64 nr_pred = hweight32(pred_mask);
+	int bit;
+
+	perf_output_put(handle, nr_vectors);
+	perf_output_put(handle, vec_qwords);
+	perf_output_put(handle, nr_pred);
+	perf_output_put(handle, pred_qwords);
+
+	if (nr_vectors) {
+		word_for_each_set_bit(bit, mask) {
+			for (int i = 0; i < vec_qwords; i++) {
+				u64 val = perf_simd_reg_value(regs, bit,
+							      i, false);
+				perf_output_put(handle, val);
+			}
+		}
+	}
+	if (nr_pred) {
+		word_for_each_set_bit(bit, pred_mask) {
+			for (int i = 0; i < pred_qwords; i++) {
+				u64 val = perf_simd_reg_value(regs, bit,
+							      i, true);
+				perf_output_put(handle, val);
+			}
+		}
+	}
+}
+
 static void perf_sample_regs_user(struct perf_regs *regs_user,
 				  struct pt_regs *regs)
 {
@@ -7828,6 +7866,22 @@ static void perf_sample_regs_intr(struct perf_regs *regs_intr,
 	regs_intr->abi  = perf_reg_abi(current);
 }
 
+int __weak perf_simd_reg_validate(u16 simd_enabled, u16 vec_qwords,
+				  u64 vec_mask_intr, u64 vec_mask_user,
+				  u16 pred_qwords, u32 pred_mask_intr,
+				  u32 pred_mask_user)
+{
+	return simd_enabled ||
+	       vec_qwords || vec_mask_intr || vec_mask_user ||
+	       pred_qwords || pred_mask_intr || pred_mask_user ?
+	       -EINVAL : 0;
+}
+
+u64 __weak perf_simd_reg_value(struct pt_regs *regs, int idx,
+			       u16 qwords_idx, bool pred)
+{
+	return 0;
+}
 
 /*
  * Get remaining task size from user stack pointer.
@@ -8358,10 +8412,17 @@ void perf_output_sample(struct perf_output_handle *handle,
 		perf_output_put(handle, abi);
 
 		if (abi) {
-			u64 mask = event->attr.sample_regs_user;
+			struct perf_event_attr *attr = &event->attr;
+			u64 mask = attr->sample_regs_user;
 			perf_output_sample_regs(handle,
 						data->regs_user.regs,
 						mask);
+			if (abi & PERF_SAMPLE_REGS_ABI_SIMD) {
+				perf_output_sample_simd_regs(handle, event,
+							     data->regs_user.regs,
+							     attr->sample_simd_vec_reg_user,
+							     attr->sample_simd_pred_reg_user);
+			}
 		}
 	}
 
@@ -8389,11 +8450,18 @@ void perf_output_sample(struct perf_output_handle *handle,
 		perf_output_put(handle, abi);
 
 		if (abi) {
-			u64 mask = event->attr.sample_regs_intr;
+			struct perf_event_attr *attr = &event->attr;
+			u64 mask = attr->sample_regs_intr;
 
 			perf_output_sample_regs(handle,
 						data->regs_intr.regs,
 						mask);
+			if (abi & PERF_SAMPLE_REGS_ABI_SIMD) {
+				perf_output_sample_simd_regs(handle, event,
+							     data->regs_intr.regs,
+							     attr->sample_simd_vec_reg_intr,
+							     attr->sample_simd_pred_reg_intr);
+			}
 		}
 	}
 
@@ -8596,6 +8664,33 @@ static __always_inline u64 __cond_set(u64 flags, u64 s, u64 d)
 	return d * !!(flags & s);
 }
 
+static u64 perf_update_xregs_size(struct perf_event *event, bool intr)
+{
+	u16 pred_qwords = event->attr.sample_simd_pred_reg_qwords;
+	u16 vec_qwords = event->attr.sample_simd_vec_reg_qwords;
+	u64 pred_mask;
+	u64 mask;
+	int size;
+
+	if (intr) {
+		mask = event->attr.sample_simd_vec_reg_intr;
+		pred_mask = event->attr.sample_simd_pred_reg_intr;
+	} else {
+		mask = event->attr.sample_simd_vec_reg_user;
+		pred_mask = event->attr.sample_simd_pred_reg_user;
+	}
+
+	/* nr_vectors, vector_qwords, nr_pred, pred_qwords */
+	size = sizeof(u64) * 4;
+	size += (hweight64(mask) * vec_qwords +
+		 hweight64(pred_mask) * pred_qwords) * sizeof(u64);
+
+	/* Warn if exceeding perf_event_header.size (u16). */
+	WARN_ON_ONCE(size > U16_MAX);
+
+	return size;
+}
+
 void perf_prepare_sample(struct perf_sample_data *data,
 			 struct perf_event *event,
 			 struct pt_regs *regs)
@@ -8661,6 +8756,11 @@ void perf_prepare_sample(struct perf_sample_data *data,
 			size += hweight64(mask) * sizeof(u64);
 		}
 
+		if (data->regs_user.abi && event_has_simd_regs(event)) {
+			size += perf_update_xregs_size(event, false);
+			data->regs_user.abi |= PERF_SAMPLE_REGS_ABI_SIMD;
+		}
+
 		data->dyn_size += size;
 		data->sample_flags |= PERF_SAMPLE_REGS_USER;
 	}
@@ -8724,6 +8824,11 @@ void perf_prepare_sample(struct perf_sample_data *data,
 			size += hweight64(mask) * sizeof(u64);
 		}
 
+		if (data->regs_intr.abi && event_has_simd_regs(event)) {
+			size += perf_update_xregs_size(event, true);
+			data->regs_intr.abi |= PERF_SAMPLE_REGS_ABI_SIMD;
+		}
+
 		data->dyn_size += size;
 		data->sample_flags |= PERF_SAMPLE_REGS_INTR;
 	}
@@ -13089,6 +13194,12 @@ static int perf_try_init_event(struct pmu *pmu, struct perf_event *event)
 	if (ret)
 		goto err_pmu;
 
+	if (!(pmu->capabilities & PERF_PMU_CAP_SIMD_REGS) &&
+	    event_has_simd_regs(event)) {
+		ret = -EOPNOTSUPP;
+		goto err_destroy;
+	}
+
 	if (!(pmu->capabilities & PERF_PMU_CAP_EXTENDED_REGS) &&
 	    event_has_extended_regs(event)) {
 		ret = -EOPNOTSUPP;
@@ -13585,7 +13696,8 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 
 	attr->size = size;
 
-	if (attr->__reserved_1 || attr->__reserved_2 || attr->__reserved_3)
+	if (attr->__reserved_1 || attr->__reserved_2 ||
+	    attr->__reserved_3 || attr->__reserved_4)
 		return -EINVAL;
 
 	if (attr->sample_type & ~(PERF_SAMPLE_MAX-1))
@@ -13634,6 +13746,15 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 		ret = perf_reg_validate(attr->sample_regs_user);
 		if (ret)
 			return ret;
+		ret = perf_simd_reg_validate(attr->sample_simd_regs_enabled,
+					     attr->sample_simd_vec_reg_qwords,
+					     attr->sample_simd_vec_reg_intr,
+					     attr->sample_simd_vec_reg_user,
+					     attr->sample_simd_pred_reg_qwords,
+					     attr->sample_simd_pred_reg_intr,
+					     attr->sample_simd_pred_reg_user);
+		if (ret)
+			return ret;
 	}
 
 	if (attr->sample_type & PERF_SAMPLE_STACK_USER) {
@@ -13654,8 +13775,20 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 	if (!attr->sample_max_stack)
 		attr->sample_max_stack = sysctl_perf_event_max_stack;
 
-	if (attr->sample_type & PERF_SAMPLE_REGS_INTR)
+	if (attr->sample_type & PERF_SAMPLE_REGS_INTR) {
 		ret = perf_reg_validate(attr->sample_regs_intr);
+		if (ret)
+			return ret;
+		ret = perf_simd_reg_validate(attr->sample_simd_regs_enabled,
+					     attr->sample_simd_vec_reg_qwords,
+					     attr->sample_simd_vec_reg_intr,
+					     attr->sample_simd_vec_reg_user,
+					     attr->sample_simd_pred_reg_qwords,
+					     attr->sample_simd_pred_reg_intr,
+					     attr->sample_simd_pred_reg_user);
+		if (ret)
+			return ret;
+	}
 
 #ifndef CONFIG_CGROUP_PERF
 	if (attr->sample_type & PERF_SAMPLE_CGROUP)
-- 
2.34.1