[PATCH v11 03/11] perf/x86/lbr: Add interface to get basic information about LBR stack

[Like Xu]

The LBR stack msrs are model specific. The perf subsystem has already
obtained the LBR stack base addresses based on the cpu model.

Therefore, an interface is added to allow callers outside the perf
subsystem to obtain the LBR stack base addresses. It's useful for
hypervisors to emulate the LBR feature for guests with less code.

Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Co-developed-by: Wei Wang <wei.w.wang@xxxxxxxxx>
Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
---
 arch/x86/events/intel/lbr.c       | 20 ++++++++++++++++++++
 arch/x86/include/asm/perf_event.h | 12 ++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 65113b16804a..6c60dcaaaf69 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1343,3 +1343,23 @@ void intel_pmu_lbr_init_knl(void)
 	if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_LIP)
 		x86_pmu.intel_cap.lbr_format = LBR_FORMAT_EIP_FLAGS;
 }
+
+/**
+ * x86_perf_get_lbr - get the LBR stack information
+ *
+ * @stack: the caller's memory to store the LBR stack information
+ *
+ * Returns: 0 indicates the LBR stack info has been successfully obtained
+ */
+int x86_perf_get_lbr(struct x86_pmu_lbr *stack)
+{
+	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
+
+	stack->nr = x86_pmu.lbr_nr;
+	stack->from = x86_pmu.lbr_from;
+	stack->to = x86_pmu.lbr_to;
+	stack->info = (lbr_fmt == LBR_FORMAT_INFO) ? MSR_LBR_INFO_0 : 0;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index e855e9cf2c37..5071515f6b0f 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -333,6 +333,13 @@ struct perf_guest_switch_msr {
 	u64 host, guest;
 };
 
+struct x86_pmu_lbr {
+	unsigned int	nr;
+	unsigned int	from;
+	unsigned int	to;
+	unsigned int	info;
+};
+
 extern void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap);
 extern void perf_check_microcode(void);
 extern int x86_perf_rdpmc_index(struct perf_event *event);
@@ -348,12 +355,17 @@ static inline void perf_check_microcode(void) { }
 
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)
 extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
+extern int x86_perf_get_lbr(struct x86_pmu_lbr *stack);
 #else
 static inline struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
 {
 	*nr = 0;
 	return NULL;
 }
+static inline int x86_perf_get_lbr(struct x86_pmu_lbr *stack)
+{
+	return -1;
+}
 #endif
 
 #ifdef CONFIG_CPU_SUP_INTEL
-- 
2.21.3