[Patch v3 3/4] perf/x86/intel/lbr: Reset the cached LBR stack in intel_pmu_lbr_reset()

[Dapeng Mi <dapeng1.mi@linux.intel.com>]

Reset the cached LBR stack in addition to the hardware LBR register file
when intel_pmu_lbr_reset() is called. This prevents stale LBR data from
being reused after a context switch or similar transition.

Also adjust intel_pmu_arch_lbr_read_xsave() to update the cached LBR
stack only when new hardware LBR data is present, avoiding overwrite of
stale data with previously captured values.

Fixes: c085fb877467 ("perf/x86/intel/lbr: Support XSAVES for arch LBR read")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
---
 arch/x86/events/intel/lbr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 0b446d8912e4..249db12e927e 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -193,6 +193,8 @@ void intel_pmu_lbr_reset(void)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
 
+	cpuc->lbr_stack.nr = 0;
+
 	if (!x86_pmu.lbr_nr)
 		return;
 
@@ -1012,7 +1014,8 @@ static void intel_pmu_arch_lbr_read_xsave(struct cpu_hw_events *cpuc)
 	}
 	xsaves(&xsave->xsave, XFEATURE_MASK_LBR);
 
-	intel_pmu_store_lbr(cpuc, xsave->lbr.entries);
+	if (xsave->header.xfeatures & XFEATURE_MASK_LBR)
+		intel_pmu_store_lbr(cpuc, xsave->lbr.entries);
 }
 
 void intel_pmu_lbr_read(void)
-- 
2.34.1