perf/x86/amd/lbr: Add LbrExtV2 software branch filter support

With AMD Last Branch Record Extension Version 2 (LbrExtV2), it is necessary
to process the branch records further as hardware filtering is not granular
enough for identifying certain types of branches. E.g. to record system
calls, one should record far branches. The filter captures both far calls
and far returns but the irrelevant records are filtered out based on the
branch type as seen by the branch classifier.
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/e51de057517f77788abd393c832e8dea616d489c.1660211399.git.sandipan.das@amd.com

arch/x86/events/amd/lbr.c

@@ -94,6 +94,50 @@ static __always_inline u64 sign_ext_branch_ip(u64 ip)
 	return (u64)(((s64)ip << shift) >> shift);
 }
 
+static void amd_pmu_lbr_filter(void)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	int br_sel = cpuc->br_sel, type, i, j;
+	bool compress = false;
+	u64 from, to;
+
+	/* If sampling all branches, there is nothing to filter */
+	if (((br_sel & X86_BR_ALL) == X86_BR_ALL) &&
+	    ((br_sel & X86_BR_TYPE_SAVE) != X86_BR_TYPE_SAVE))
+		return;
+
+	for (i = 0; i < cpuc->lbr_stack.nr; i++) {
+		from = cpuc->lbr_entries[i].from;
+		to = cpuc->lbr_entries[i].to;
+		type = branch_type(from, to, 0);
+
+		/* If type does not correspond, then discard */
+		if (type == X86_BR_NONE || (br_sel & type) != type) {
+			cpuc->lbr_entries[i].from = 0;	/* mark invalid */
+			compress = true;
+		}
+
+		if ((br_sel & X86_BR_TYPE_SAVE) == X86_BR_TYPE_SAVE)
+			cpuc->lbr_entries[i].type = common_branch_type(type);
+	}
+
+	if (!compress)
+		return;
+
+	/* Remove all invalid entries */
+	for (i = 0; i < cpuc->lbr_stack.nr; ) {
+		if (!cpuc->lbr_entries[i].from) {
+			j = i;
+			while (++j < cpuc->lbr_stack.nr)
+				cpuc->lbr_entries[j - 1] = cpuc->lbr_entries[j];
+			cpuc->lbr_stack.nr--;
+			if (!cpuc->lbr_entries[i].from)
+				continue;
+		}
+		i++;
+	}
+}
+
 void amd_pmu_lbr_read(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
@@ -128,6 +172,9 @@ void amd_pmu_lbr_read(void)
 	 * LBR To[0] always represent the TOS
 	 */
 	cpuc->lbr_stack.hw_idx = 0;
+
+	/* Perform further software filtering */
+	amd_pmu_lbr_filter();
 }
 
 static const int lbr_select_map[PERF_SAMPLE_BRANCH_MAX_SHIFT] = {
@@ -136,8 +183,8 @@ static const int lbr_select_map[PERF_SAMPLE_BRANCH_MAX_SHIFT] = {
 	[PERF_SAMPLE_BRANCH_HV_SHIFT]		= LBR_IGNORE,
 
 	[PERF_SAMPLE_BRANCH_ANY_SHIFT]		= LBR_ANY,
-	[PERF_SAMPLE_BRANCH_ANY_CALL_SHIFT]	= LBR_REL_CALL | LBR_IND_CALL,
-	[PERF_SAMPLE_BRANCH_ANY_RETURN_SHIFT]	= LBR_RETURN,
+	[PERF_SAMPLE_BRANCH_ANY_CALL_SHIFT]	= LBR_REL_CALL | LBR_IND_CALL | LBR_FAR,
+	[PERF_SAMPLE_BRANCH_ANY_RETURN_SHIFT]	= LBR_RETURN | LBR_FAR,
 	[PERF_SAMPLE_BRANCH_IND_CALL_SHIFT]	= LBR_IND_CALL,
 	[PERF_SAMPLE_BRANCH_ABORT_TX_SHIFT]	= LBR_NOT_SUPP,
 	[PERF_SAMPLE_BRANCH_IN_TX_SHIFT]	= LBR_NOT_SUPP,
@@ -150,8 +197,6 @@ static const int lbr_select_map[PERF_SAMPLE_BRANCH_MAX_SHIFT] = {
 
 	[PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT]	= LBR_NOT_SUPP,
 	[PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT]	= LBR_NOT_SUPP,
-
-	[PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT]	= LBR_NOT_SUPP,
 };
 
 static int amd_pmu_lbr_setup_filter(struct perf_event *event)
@@ -165,6 +210,41 @@ static int amd_pmu_lbr_setup_filter(struct perf_event *event)
 	if (!x86_pmu.lbr_nr)
 		return -EOPNOTSUPP;
 
+	if (br_type & PERF_SAMPLE_BRANCH_USER)
+		mask |= X86_BR_USER;
+
+	if (br_type & PERF_SAMPLE_BRANCH_KERNEL)
+		mask |= X86_BR_KERNEL;
+
+	/* Ignore BRANCH_HV here */
+
+	if (br_type & PERF_SAMPLE_BRANCH_ANY)
+		mask |= X86_BR_ANY;
+
+	if (br_type & PERF_SAMPLE_BRANCH_ANY_CALL)
+		mask |= X86_BR_ANY_CALL;
+
+	if (br_type & PERF_SAMPLE_BRANCH_ANY_RETURN)
+		mask |= X86_BR_RET | X86_BR_IRET | X86_BR_SYSRET;
+
+	if (br_type & PERF_SAMPLE_BRANCH_IND_CALL)
+		mask |= X86_BR_IND_CALL;
+
+	if (br_type & PERF_SAMPLE_BRANCH_COND)
+		mask |= X86_BR_JCC;
+
+	if (br_type & PERF_SAMPLE_BRANCH_IND_JUMP)
+		mask |= X86_BR_IND_JMP;
+
+	if (br_type & PERF_SAMPLE_BRANCH_CALL)
+		mask |= X86_BR_CALL | X86_BR_ZERO_CALL;
+
+	if (br_type & PERF_SAMPLE_BRANCH_TYPE_SAVE)
+		mask |= X86_BR_TYPE_SAVE;
+
+	reg->reg = mask;
+	mask = 0;
+
 	for (i = 0; i < PERF_SAMPLE_BRANCH_MAX_SHIFT; i++) {
 		if (!(br_type & BIT_ULL(i)))
 			continue;
@@ -220,13 +300,15 @@ void amd_pmu_lbr_reset(void)
 void amd_pmu_lbr_add(struct perf_event *event)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct hw_perf_event_extra *reg = &event->hw.branch_reg;
 
 	if (!x86_pmu.lbr_nr)
 		return;
 
 	if (has_branch_stack(event)) {
 		cpuc->lbr_select = 1;
-		cpuc->lbr_sel->config = event->hw.branch_reg.config;
+		cpuc->lbr_sel->config = reg->config;
+		cpuc->br_sel = reg->reg;
 	}
 
 	perf_sched_cb_inc(event->ctx->pmu);