linux-kernel - [PATCH v1 3/4] perf/x86: add a function to get the lbr stack

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Date:   Mon, 25 Sep 2017 12:44:55 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com, mst@...hat.com,
        rkrcmar@...hat.com, ak@...ux.intel.com, mingo@...hat.com
Cc:     Wei Wang <wei.w.wang@...el.com>
Subject: [PATCH v1 3/4] perf/x86: add a function to get the lbr stack

The LBR stack MSRs are architecturally specific. The perf subsystem has
already assigned the abstracted MSR values based on the CPU architecture.

This patch enables a caller outside the perf subsystem to get the LBR
stack info. This is useful for hyperviosrs to prepare the lbr feature
for the guest.

Signed-off-by: Wei Wang <wei.w.wang@...el.com>
---
 arch/x86/events/intel/lbr.c       | 23 +++++++++++++++++++++++
 arch/x86/include/asm/perf_event.h | 14 ++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 8a6bbac..ea547ec 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1230,3 +1230,26 @@ void intel_pmu_lbr_init_knl(void)
 	x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
 	x86_pmu.lbr_sel_map  = snb_lbr_sel_map;
 }
+
+/**
+ * perf_get_lbr_stack - get the lbr stack related MSRs
+ *
+ * @stack: the caller's memory to get the lbr stack
+ *
+ * Returns: 0 indicates that the lbr stack has been successfully obtained.
+ */
+int perf_get_lbr_stack(struct perf_lbr_stack *stack)
+{
+	stack->lbr_nr = x86_pmu.lbr_nr;
+	stack->lbr_tos = x86_pmu.lbr_tos;
+	stack->lbr_from = x86_pmu.lbr_from;
+	stack->lbr_to = x86_pmu.lbr_to;
+
+	if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_INFO)
+		stack->lbr_info = MSR_LBR_INFO_0;
+	else
+		stack->lbr_info = 0;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(perf_get_lbr_stack);
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index f353061..c098462 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -266,7 +266,16 @@ struct perf_guest_switch_msr {
 	u64 host, guest;
 };
 
+struct perf_lbr_stack {
+	int		lbr_nr;
+	unsigned long	lbr_tos;
+	unsigned long	lbr_from;
+	unsigned long	lbr_to;
+	unsigned long	lbr_info;
+};
+
 extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
+extern int perf_get_lbr_stack(struct perf_lbr_stack *stack);
 extern void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap);
 extern void perf_check_microcode(void);
 #else
@@ -276,6 +285,11 @@ static inline struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
 	return NULL;
 }
 
+static inline int perf_get_lbr_stack(struct perf_lbr_stack *stack)
+{
+	return -1;
+}
+
 static inline void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
 {
 	memset(cap, 0, sizeof(*cap));
-- 
2.7.4