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From:   Sandipan Das <sandipan.das@amd.com>
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Subject: [PATCH 05/13] perf/x86/amd/lbr: Detect LbrExtV2 support
Date:   Thu, 11 Aug 2022 17:59:53 +0530
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AMD Last Branch Record Extension Version 2 (LbrExtV2) is driven by Core PMC
overflows. It records recently taken branches up to the moment when the PMC
overflow occurs.

Detect the feature during PMU initialization and set the branch stack depth
using CPUID leaf 0x80000022 EBX.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
---
 arch/x86/events/amd/Makefile      |  2 +-
 arch/x86/events/amd/core.c        |  9 +++++----
 arch/x86/events/amd/lbr.c         | 21 +++++++++++++++++++++
 arch/x86/events/perf_event.h      |  2 ++
 arch/x86/include/asm/perf_event.h |  3 ++-
 5 files changed, 31 insertions(+), 6 deletions(-)
 create mode 100644 arch/x86/events/amd/lbr.c

diff --git a/arch/x86/events/amd/Makefile b/arch/x86/events/amd/Makefile
index b9f5d4610256..527d947eb76b 100644
--- a/arch/x86/events/amd/Makefile
+++ b/arch/x86/events/amd/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_CPU_SUP_AMD)		+= core.o
+obj-$(CONFIG_CPU_SUP_AMD)		+= core.o lbr.o
 obj-$(CONFIG_PERF_EVENTS_AMD_BRS)	+= brs.o
 obj-$(CONFIG_PERF_EVENTS_AMD_POWER)	+= power.o
 obj-$(CONFIG_X86_LOCAL_APIC)		+= ibs.o
diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index ef3520731a20..a3aa67b4fd50 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -1374,10 +1374,11 @@ static int __init amd_core_pmu_init(void)
 		x86_pmu.flags |= PMU_FL_PAIR;
 	}
 
-	/*
-	 * BRS requires special event constraints and flushing on ctxsw.
-	 */
-	if (boot_cpu_data.x86 >= 0x19 && !amd_brs_init()) {
+	/* LBR and BRS are mutually exclusive features */
+	if (amd_pmu_lbr_init() && !amd_brs_init()) {
+		/*
+		 * BRS requires special event constraints and flushing on ctxsw.
+		 */
 		x86_pmu.get_event_constraints = amd_get_event_constraints_f19h;
 		x86_pmu.sched_task = amd_pmu_brs_sched_task;
 		x86_pmu.limit_period = amd_pmu_limit_period;
diff --git a/arch/x86/events/amd/lbr.c b/arch/x86/events/amd/lbr.c
new file mode 100644
index 000000000000..d240ff722b78
--- /dev/null
+++ b/arch/x86/events/amd/lbr.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/perf_event.h>
+#include <asm/perf_event.h>
+
+#include "../perf_event.h"
+
+__init int amd_pmu_lbr_init(void)
+{
+	union cpuid_0x80000022_ebx ebx;
+
+	if (x86_pmu.version < 2 || !boot_cpu_has(X86_FEATURE_LBREXT_V2))
+		return -EOPNOTSUPP;
+
+	/* Set number of entries */
+	ebx.full = cpuid_ebx(EXT_PERFMON_DEBUG_FEATURES);
+	x86_pmu.lbr_nr = ebx.split.lbr_v2_stack_sz;
+
+	pr_cont("%d-deep LBR, ", x86_pmu.lbr_nr);
+
+	return 0;
+}
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 6d23e88d232c..a6cd83c57e8b 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1230,6 +1230,8 @@ static inline bool fixed_counter_disabled(int i, struct pmu *pmu)
 
 int amd_pmu_init(void);
 
+int amd_pmu_lbr_init(void);
+
 #ifdef CONFIG_PERF_EVENTS_AMD_BRS
 
 #define AMD_FAM19H_BRS_EVENT 0xc4 /* RETIRED_TAKEN_BRANCH_INSTRUCTIONS */
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 34348ae41cdb..07844424aaea 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -207,7 +207,8 @@ union cpuid_0x80000022_ebx {
 	struct {
 		/* Number of Core Performance Counters */
 		unsigned int	num_core_pmc:4;
-		unsigned int	reserved:6;
+		/* Number of available LBR Stack Entries */
+		unsigned int	lbr_v2_stack_sz:6;
 		/* Number of Data Fabric Counters */
 		unsigned int	num_df_pmc:6;
 	} split;
-- 
2.34.1