[RFC PATCH v2 2/3] perf/x86/intel/pt: Introduce and export pt_get_curr_event()

[Xiaoyao Li]

KVM supports PT_MODE_HOST_GUEST mode for Intel PT where host and guest
have separate Intel PT configurations and they work independently.

Currently, in this mode, when both host and guest enable PT, KVM manually
clears MSR_IA32_RTIT_CTL.TRACEEN to disable host PT so that it can
context switch the other PT MSRs. However, PT PMI can be delivered after
this point and before the VM-entry. As a result, the re-enabling of PT
leads to VM-entry failure of guest.

To solve the problem, introduce and export pt_get_curr_event() for KVM
to get current pt event. Along with perf_event_{dis, en}able_local(),
With them, KVM can avoid PT re-enabling in PT PMI handler.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
 arch/x86/events/intel/pt.c        | 8 ++++++++
 arch/x86/include/asm/perf_event.h | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 82ef87e9a897..62bfc45c11c9 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1624,6 +1624,14 @@ static void pt_event_stop(struct perf_event *event, int mode)
 	}
 }
 
+struct perf_event *pt_get_curr_event(void)
+{
+	struct pt *pt = this_cpu_ptr(&pt_ctx);
+
+	return pt->handle.event;
+}
+EXPORT_SYMBOL_GPL(pt_get_curr_event);
+
 static long pt_event_snapshot_aux(struct perf_event *event,
 				  struct perf_output_handle *handle,
 				  unsigned long size)
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index f6fc8dd51ef4..7c3533392cf5 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -553,11 +553,13 @@ static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 
 #ifdef CONFIG_CPU_SUP_INTEL
  extern void intel_pt_handle_vmx(int on);
+ extern struct perf_event *pt_get_curr_event(void);
 #else
 static inline void intel_pt_handle_vmx(int on)
 {
 
 }
+struct perf_event *pt_get_curr_event(void) { return NULL; }
 #endif
 
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_AMD)
-- 
2.27.0