[tip: perf/core] perf/x86: Remove stale fixed counter helper and fix hybrid PMU access

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     3ba87c5bf11bea80e56abe17730085bc962ecfbe
Gitweb:        https://git.kernel.org/tip/3ba87c5bf11bea80e56abe17730085bc962ecfbe
Author:        Dapeng Mi <[email protected]>
AuthorDate:    Fri, 17 Jul 2026 16:03:39 +08:00
Committer:     Peter Zijlstra <[email protected]>
CommitterDate: Mon, 10 Aug 2026 15:05:48 +02:00

perf/x86: Remove stale fixed counter helper and fix hybrid PMU access

On hybrid systems, init_hw_perf_events() can call check_hw_exists() with
the global PMU pointer after perf_is_hybrid is set. In that case,
fixed_counter_disabled() uses hybrid() on a non-hybrid PMU object, so the
intel_ctrl access is taken from the wrong layout and can read out of
bounds.

fixed_counter_disabled() was added in commit 32451614da2a
("perf/x86/intel: Support CPUID 10.ECX to disable fixed counters"), when
fixed counters were tracked via num_fixed_counters. Today fixed counters
are represented by fixed_cntr_mask, so this helper is obsolete.

Remove fixed_counter_disabled() and its callers, and rely directly on the
fixed-counter bitmask. With the helper gone, check_hw_exists() no longer
needs a PMU argument, so drop that parameter as well. This removes the
invalid hybrid access and closes the out-of-bounds read risk.

Signed-off-by: Dapeng Mi <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Thomas Falcon <[email protected]>
Reviewed-by: Zide Chen <[email protected]>
Link: https://patch.msgid.link/[email protected]
---
 arch/x86/events/core.c       |  8 ++------
 arch/x86/events/intel/core.c |  4 +---
 arch/x86/events/perf_event.h |  9 +--------
 3 files changed, 4 insertions(+), 17 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index a02f303..143a6e7 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -265,7 +265,7 @@ static void release_pmc_hardware(void) {}
 
 #endif
 
-bool check_hw_exists(struct pmu *pmu, unsigned long *cntr_mask,
+bool check_hw_exists(unsigned long *cntr_mask,
 		     unsigned long *fixed_cntr_mask)
 {
 	u64 val, val_fail = -1, val_new= ~0;
@@ -297,8 +297,6 @@ bool check_hw_exists(struct pmu *pmu, unsigned long *cntr_mask,
 		if (ret)
 			goto msr_fail;
 		for_each_set_bit(i, fixed_cntr_mask, X86_PMC_IDX_MAX) {
-			if (fixed_counter_disabled(i, pmu))
-				continue;
 			if (val & (0x03ULL << i*4)) {
 				bios_fail = 1;
 				val_fail = val;
@@ -1618,8 +1616,6 @@ void perf_event_print_debug(void)
 			cpu, idx, prev_left);
 	}
 	for_each_set_bit(idx, fixed_cntr_mask, X86_PMC_IDX_MAX) {
-		if (fixed_counter_disabled(idx, cpuc->pmu))
-			continue;
 		rdmsrq(x86_pmu_fixed_ctr_addr(idx), pmc_count);
 
 		pr_info("CPU#%d: fixed-PMC%d count: %016llx\n",
@@ -2180,7 +2176,7 @@ static int __init init_hw_perf_events(void)
 	pmu_check_apic();
 
 	/* sanity check that the hardware exists or is emulated */
-	if (!check_hw_exists(&pmu, x86_pmu.cntr_mask, x86_pmu.fixed_cntr_mask))
+	if (!check_hw_exists(x86_pmu.cntr_mask, x86_pmu.fixed_cntr_mask))
 		goto out_bad_pmu;
 
 	pr_cont("%s PMU driver.\n", x86_pmu.name);
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index b47d2f0..c418176 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3713,8 +3713,6 @@ static void intel_pmu_reset(void)
 		wrmsrq_safe(x86_pmu_event_addr(idx),  0ull);
 	}
 	for_each_set_bit(idx, fixed_cntr_mask, INTEL_PMC_MAX_FIXED) {
-		if (fixed_counter_disabled(idx, cpuc->pmu))
-			continue;
 		wrmsrq_safe(x86_pmu_fixed_ctr_addr(idx), 0ull);
 	}
 
@@ -6336,7 +6334,7 @@ static bool init_hybrid_pmu(int cpu)
 
 	intel_pmu_check_hybrid_pmus(pmu);
 
-	if (!check_hw_exists(&pmu->pmu, pmu->cntr_mask, pmu->fixed_cntr_mask)) {
+	if (!check_hw_exists(pmu->cntr_mask, pmu->fixed_cntr_mask)) {
 		cpuc->pmu = NULL;
 		return false;
 	}
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 01ae287..cc9cfaa 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1243,7 +1243,7 @@ static inline int x86_pmu_rdpmc_index(int index)
 	return x86_pmu.rdpmc_index ? x86_pmu.rdpmc_index(index) : index;
 }
 
-bool check_hw_exists(struct pmu *pmu, unsigned long *cntr_mask,
+bool check_hw_exists(unsigned long *cntr_mask,
 		     unsigned long *fixed_cntr_mask);
 
 int x86_add_exclusive(unsigned int what);
@@ -1456,13 +1456,6 @@ ssize_t events_hybrid_sysfs_show(struct device *dev,
 				 struct device_attribute *attr,
 				 char *page);
 
-static inline bool fixed_counter_disabled(int i, struct pmu *pmu)
-{
-	u64 intel_ctrl = hybrid(pmu, intel_ctrl);
-
-	return !(intel_ctrl >> (i + INTEL_PMC_IDX_FIXED));
-}
-
 #ifdef CONFIG_CPU_SUP_AMD
 
 int amd_pmu_init(void);