perf/x86/intel: Clean up PEBS-via-PT on hybrid

BugLink: https://bugs.launchpad.net/bugs/2104873

[ Upstream commit 0a55615 ]

The PEBS-via-PT feature is exposed for the e-core of some hybrid
platforms, e.g., ADL and MTL. But it never works.

$ dmesg | grep PEBS
[    1.793888] core: cpu_atom PMU driver: PEBS-via-PT

$ perf record -c 1000 -e '{intel_pt/branch=0/,
cpu_atom/cpu-cycles,aux-output/pp}' -C8
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument)
for event (cpu_atom/cpu-cycles,aux-output/pp).
"dmesg | grep -i perf" may provide additional information.

The "PEBS-via-PT" is printed if the corresponding bit of per-PMU
capabilities is set. Since the feature is supported by the e-core HW,
perf sets the bit for e-core. However, for Intel PT, if a feature is not
supported on all CPUs, it is not supported at all. The PEBS-via-PT event
cannot be created successfully.

The PEBS-via-PT is no longer enumerated on the latest hybrid platform. It
will be deprecated on future platforms with Arch PEBS. Let's remove it
from the existing hybrid platforms.

Fixes: d9977c4 ("perf/x86: Register hybrid PMUs")
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250129154820.3755948-2-kan.liang@linux.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Noah Wager <noah.wager@canonical.com>

Author: Kan Liang

arch/x86/events/intel/core.c

@@ -4901,11 +4901,6 @@ static void intel_pmu_check_hybrid_pmus(struct x86_hybrid_pmu *pmu)
 	else
 		pmu->intel_ctrl &= ~(1ULL << GLOBAL_CTRL_EN_PERF_METRICS);
 
-	if (pmu->intel_cap.pebs_output_pt_available)
-		pmu->pmu.capabilities |= PERF_PMU_CAP_AUX_OUTPUT;
-	else
-		pmu->pmu.capabilities &= ~PERF_PMU_CAP_AUX_OUTPUT;
-
 	intel_pmu_check_event_constraints(pmu->event_constraints,
 					  pmu->cntr_mask64,
 					  pmu->fixed_cntr_mask64,
@@ -4974,9 +4969,6 @@ static bool init_hybrid_pmu(int cpu)
 
 	pr_info("%s PMU driver: ", pmu->name);
 
-	if (pmu->intel_cap.pebs_output_pt_available)
-		pr_cont("PEBS-via-PT ");
-
 	pr_cont("\n");
 
 	x86_pmu_show_pmu_cap(&pmu->pmu);
@@ -6287,11 +6279,9 @@ static __always_inline int intel_pmu_init_hybrid(enum hybrid_pmu_type pmus)
 		pmu->intel_cap.capabilities = x86_pmu.intel_cap.capabilities;
 		if (pmu->pmu_type & hybrid_small) {
 			pmu->intel_cap.perf_metrics = 0;
-			pmu->intel_cap.pebs_output_pt_available = 1;
 			pmu->mid_ack = true;
 		} else if (pmu->pmu_type & hybrid_big) {
 			pmu->intel_cap.perf_metrics = 1;
-			pmu->intel_cap.pebs_output_pt_available = 0;
 			pmu->late_ack = true;
 		}
 	}

arch/x86/events/intel/ds.c

@@ -2523,7 +2523,15 @@ void __init intel_ds_init(void)
 			}
 			pr_cont("PEBS fmt4%c%s, ", pebs_type, pebs_qual);
 
-			if (!is_hybrid() && x86_pmu.intel_cap.pebs_output_pt_available) {
+			/*
+			 * The PEBS-via-PT is not supported on hybrid platforms,
+			 * because not all CPUs of a hybrid machine support it.
+			 * The global x86_pmu.intel_cap, which only contains the
+			 * common capabilities, is used to check the availability
+			 * of the feature. The per-PMU pebs_output_pt_available
+			 * in a hybrid machine should be ignored.
+			 */
+			if (x86_pmu.intel_cap.pebs_output_pt_available) {
 				pr_cont("PEBS-via-PT, ");
 				x86_get_pmu(smp_processor_id())->capabilities |= PERF_PMU_CAP_AUX_OUTPUT;
 			}