[PATCH 0/3] perf/x86: Fix perf_event_print_debug() on non-Intel PMUs

[PATCH 0/3] perf/x86: Fix perf_event_print_debug() on non-Intel PMUs

[Sandipan Das]

Petr Tesarik reported that reading MSR_ARCH_PERFMON_FIXED_CTR_CTRL
raises a #GP on AMD processors that support PerfMonV2, and proposed
skipping that register when no fixed counters are implemented [1].

However, perf_event_print_debug() also dumps the global control and
status registers whenever x86_pmu.version >= 2, and reads Intel
Architectural PerfMon MSRs to do so. That condition used to be
Intel-specific, but since commit 21d59e3e2c40 ("perf/x86/amd/core:
Detect PerfMonV2 support"), x86_pmu.version is also set to 2 on AMD
processors that support PerfMonV2, where none of those registers are
available.

The same reasoning therefore applies to the other registers read here,
so rather than special-casing each one or reinstating a vendor check,
this series makes the global register dump a vendor-specific operation.

[1] https://lore.kernel.org/all/20260717150315.2868314-1-ptesarik@suse.com/

Sandipan Das (3):
  perf/x86: Add x86_pmu::print_debug
  perf/x86: Move MSR_CORE_PERF_GLOBAL_* dump to vendor code
  perf/x86/amd: Implement x86_pmu::print_debug

 arch/x86/events/amd/core.c     | 20 ++++++++++++
 arch/x86/events/core.c         | 56 +++++++++++++++-------------------
 arch/x86/events/intel/core.c   | 32 +++++++++++++++++++
 arch/x86/events/perf_event.h   |  4 +++
 arch/x86/events/zhaoxin/core.c | 18 +++++++++++
 5 files changed, 98 insertions(+), 32 deletions(-)

-- 
2.53.0

[PATCH 1/3] perf/x86: Add x86_pmu::print_debug

[Sandipan Das]

perf_event_print_debug() dumps the global control and status MSRs
whenever x86_pmu.version >= 2, reading registers that exist only on
Intel-compatible PMUs. This is not safe since x86_pmu.version is not
Intel-specific and is now set by other vendors whose global registers
use different addresses.

As a first step, split perf_event_print_debug() in two. The register
dump moves into a new common helper, x86_pmu_print_debug(), leaving
perf_event_print_debug() to handle the preamble and dispatch to an
optional x86_pmu::print_debug method. This lets each vendor-specific
PMU dump its own global state before chaining into the common helper.
PMUs that do not implement the method, such as those with
x86_pmu.version < 2, get the common helper alone.

No functional change intended.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
---
 arch/x86/events/core.c       | 29 ++++++++++++++++++++++-------
 arch/x86/events/perf_event.h |  4 ++++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index af0b67ffb43d..17dc53a62378 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1557,7 +1557,7 @@ static void x86_pmu_start(struct perf_event *event, int flags)
 	perf_event_update_userpage(event);
 }
 
-void perf_event_print_debug(void)
+void x86_pmu_print_debug(int cpu)
 {
 	u64 ctrl, status, overflow, pmc_ctrl, pmc_count, prev_left, fixed;
 	unsigned long *cntr_mask, *fixed_cntr_mask;
@@ -1566,17 +1566,11 @@ void perf_event_print_debug(void)
 	u64 pebs, debugctl;
 	int cpu, idx;
 
-	guard(irqsave)();
-
-	cpu = smp_processor_id();
 	cpuc = &per_cpu(cpu_hw_events, cpu);
 	cntr_mask = hybrid(cpuc->pmu, cntr_mask);
 	fixed_cntr_mask = hybrid(cpuc->pmu, fixed_cntr_mask);
 	pebs_constraints = hybrid(cpuc->pmu, pebs_constraints);
 
-	if (!*(u64 *)cntr_mask)
-		return;
-
 	if (x86_pmu.version >= 2) {
 		rdmsrq(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
 		rdmsrq(MSR_CORE_PERF_GLOBAL_STATUS, status);
@@ -1622,6 +1616,27 @@ void perf_event_print_debug(void)
 	}
 }
 
+void perf_event_print_debug(void)
+{
+	struct cpu_hw_events *cpuc;
+	unsigned long *cntr_mask;
+	int cpu;
+
+	guard(irqsave)();
+
+	cpu = smp_processor_id();
+	cpuc = &per_cpu(cpu_hw_events, cpu);
+	cntr_mask = hybrid(cpuc->pmu, cntr_mask);
+
+	if (!*(u64 *)cntr_mask)
+		return;
+
+	if (x86_pmu.print_debug)
+		x86_pmu.print_debug(cpu);
+	else
+		x86_pmu_print_debug(cpu);
+}
+
 void x86_pmu_stop(struct perf_event *event, int flags)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index a8afea8d38f0..465bf513bb82 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -1052,6 +1052,8 @@ struct x86_pmu {
 	int				num_hybrid_pmus;
 	struct x86_hybrid_pmu		*hybrid_pmu;
 	enum intel_cpu_type (*get_hybrid_cpu_type)	(void);
+
+	void (*print_debug)(int cpu);
 };
 
 struct x86_perf_task_context_opt {
@@ -1316,6 +1318,8 @@ int x86_pmu_handle_irq(struct pt_regs *regs);
 
 void x86_pmu_show_pmu_cap(struct pmu *pmu);
 
+void x86_pmu_print_debug(int cpu);
+
 static inline int x86_pmu_num_counters(struct pmu *pmu)
 {
 	return hweight64(hybrid(pmu, cntr_mask64));
-- 
2.53.0

[PATCH 2/3] perf/x86: Move MSR_CORE_PERF_GLOBAL_* dump to vendor code

[Sandipan Das]

MSR_CORE_PERF_GLOBAL_{CTRL,STATUS} and MSR_ARCH_PERFMON_FIXED_CTR_CTRL
are Intel Architectural PerfMon registers that are not available on AMD
processors.

Since commit 21d59e3e2c40 ("perf/x86/amd/core: Detect PerfMonV2
support"), x86_pmu.version is also set to 2 on AMD processors that
support PerfMonV2, which makes perf_event_print_debug() attempt to read
these non-existent MSRs. The resulting #GP is caught by the exception
fixup, but as the reads are unchecked, SysRq-P logs an "unchecked MSR
access error" for each one and then prints zeroes as if they were valid
register contents.

Implement x86_pmu::print_debug for the Intel and Zhaoxin PMUs, which do
have these registers, and drop the reads from common code. Both are
wired up through PMU descriptors that are selected only when the PMU
version is at least 2, so the version check is no longer needed.

MSR_CORE_PERF_GLOBAL_OVF_CTRL is also dropped from the dump since it is
write-to-clear and does not read back the overflow state.

Fixes: 21d59e3e2c40 ("perf/x86/amd/core: Detect PerfMonV2 support")
Reported-by: Petr Tesarik <ptesarik@suse.com>
Closes: https://lore.kernel.org/all/20260717150315.2868314-1-ptesarik@suse.com/
Cc: stable@vger.kernel.org
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
---
 arch/x86/events/core.c         | 29 +++--------------------------
 arch/x86/events/intel/core.c   | 32 ++++++++++++++++++++++++++++++++
 arch/x86/events/zhaoxin/core.c | 18 ++++++++++++++++++
 3 files changed, 53 insertions(+), 26 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 17dc53a62378..7511197579fd 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -1559,38 +1559,15 @@ static void x86_pmu_start(struct perf_event *event, int flags)
 
 void x86_pmu_print_debug(int cpu)
 {
-	u64 ctrl, status, overflow, pmc_ctrl, pmc_count, prev_left, fixed;
 	unsigned long *cntr_mask, *fixed_cntr_mask;
-	struct event_constraint *pebs_constraints;
+	u64 pmc_ctrl, pmc_count, prev_left;
 	struct cpu_hw_events *cpuc;
-	u64 pebs, debugctl;
-	int cpu, idx;
+	int idx;
 
 	cpuc = &per_cpu(cpu_hw_events, cpu);
 	cntr_mask = hybrid(cpuc->pmu, cntr_mask);
 	fixed_cntr_mask = hybrid(cpuc->pmu, fixed_cntr_mask);
-	pebs_constraints = hybrid(cpuc->pmu, pebs_constraints);
-
-	if (x86_pmu.version >= 2) {
-		rdmsrq(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
-		rdmsrq(MSR_CORE_PERF_GLOBAL_STATUS, status);
-		rdmsrq(MSR_CORE_PERF_GLOBAL_OVF_CTRL, overflow);
-		rdmsrq(MSR_ARCH_PERFMON_FIXED_CTR_CTRL, fixed);
-
-		pr_info("\n");
-		pr_info("CPU#%d: ctrl:       %016llx\n", cpu, ctrl);
-		pr_info("CPU#%d: status:     %016llx\n", cpu, status);
-		pr_info("CPU#%d: overflow:   %016llx\n", cpu, overflow);
-		pr_info("CPU#%d: fixed:      %016llx\n", cpu, fixed);
-		if (pebs_constraints) {
-			rdmsrq(MSR_IA32_PEBS_ENABLE, pebs);
-			pr_info("CPU#%d: pebs:       %016llx\n", cpu, pebs);
-		}
-		if (x86_pmu.lbr_nr) {
-			rdmsrq(MSR_IA32_DEBUGCTLMSR, debugctl);
-			pr_info("CPU#%d: debugctl:   %016llx\n", cpu, debugctl);
-		}
-	}
+
 	pr_info("CPU#%d: active:     %016llx\n", cpu, *(u64 *)cpuc->active_mask);
 
 	for_each_set_bit(idx, cntr_mask, X86_PMC_IDX_MAX) {
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index b39c6ce0efb5..e1ed0e173d0c 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3736,6 +3736,36 @@ static void intel_pmu_reset(void)
 	local_irq_restore(flags);
 }
 
+static void intel_pmu_print_debug(int cpu)
+{
+	struct event_constraint *pebs_constraints;
+	struct cpu_hw_events *cpuc;
+	u64 ctrl, status, fixed;
+	u64 pebs, debugctl;
+
+	cpuc = &per_cpu(cpu_hw_events, cpu);
+	pebs_constraints = hybrid(cpuc->pmu, pebs_constraints);
+
+	rdmsrq(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
+	rdmsrq(MSR_CORE_PERF_GLOBAL_STATUS, status);
+	rdmsrq(MSR_ARCH_PERFMON_FIXED_CTR_CTRL, fixed);
+
+	pr_info("\n");
+	pr_info("CPU#%d: ctrl:       %016llx\n", cpu, ctrl);
+	pr_info("CPU#%d: status:     %016llx\n", cpu, status);
+	pr_info("CPU#%d: fixed:      %016llx\n", cpu, fixed);
+	if (pebs_constraints) {
+		rdmsrq(MSR_IA32_PEBS_ENABLE, pebs);
+		pr_info("CPU#%d: pebs:       %016llx\n", cpu, pebs);
+	}
+	if (x86_pmu.lbr_nr) {
+		rdmsrq(MSR_IA32_DEBUGCTLMSR, debugctl);
+		pr_info("CPU#%d: debugctl:   %016llx\n", cpu, debugctl);
+	}
+
+	x86_pmu_print_debug(cpu);
+}
+
 /*
  * We may be running with guest PEBS events created by KVM, and the
  * PEBS records are logged into the guest's DS and invisible to host.
@@ -6680,6 +6710,8 @@ static __initconst const struct x86_pmu intel_pmu = {
 	 * counting SMM by default.
 	 */
 	.attr_freeze_on_smi	= 1,
+
+	.print_debug		= intel_pmu_print_debug,
 };
 
 static __init void intel_clovertown_quirk(void)
diff --git a/arch/x86/events/zhaoxin/core.c b/arch/x86/events/zhaoxin/core.c
index e506f677db57..cc447e228efb 100644
--- a/arch/x86/events/zhaoxin/core.c
+++ b/arch/x86/events/zhaoxin/core.c
@@ -288,6 +288,22 @@ static inline void zxc_pmu_ack_status(u64 ack)
 	zhaoxin_pmu_disable_all();
 }
 
+static void zhaoxin_pmu_print_debug(int cpu)
+{
+	u64 ctrl, status, fixed;
+
+	rdmsrq(MSR_CORE_PERF_GLOBAL_CTRL, ctrl);
+	rdmsrq(MSR_CORE_PERF_GLOBAL_STATUS, status);
+	rdmsrq(MSR_ARCH_PERFMON_FIXED_CTR_CTRL, fixed);
+
+	pr_info("\n");
+	pr_info("CPU#%d: ctrl:       %016llx\n", cpu, ctrl);
+	pr_info("CPU#%d: status:     %016llx\n", cpu, status);
+	pr_info("CPU#%d: fixed:      %016llx\n", cpu, fixed);
+
+	x86_pmu_print_debug(cpu);
+}
+
 static void zhaoxin_pmu_disable_fixed(struct hw_perf_event *hwc)
 {
 	int idx = hwc->idx - INTEL_PMC_IDX_FIXED;
@@ -479,6 +495,8 @@ static const struct x86_pmu zhaoxin_pmu __initconst = {
 
 	.format_attrs		= zx_arch_formats_attr,
 	.events_sysfs_show	= zhaoxin_event_sysfs_show,
+
+	.print_debug		= zhaoxin_pmu_print_debug,
 };
 
 static const struct { int id; char *name; } zx_arch_events_map[] __initconst = {
-- 
2.53.0

[PATCH 3/3] perf/x86/amd: Implement x86_pmu::print_debug

[Sandipan Das]

Implement x86_pmu::print_debug for PerfMonV2 capable processors to dump
MSR_AMD64_PERF_CNTR_GLOBAL_{CTL,STATUS}, plus MSR_AMD_DBG_EXTN_CFG if
LBR Extension Version 2 is available. Chain into x86_pmu_print_debug()
afterwards to dump the event selectors and counters.

MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_{CLR,SET} are left out since they are
write-only.

Fixes: 21d59e3e2c40 ("perf/x86/amd/core: Detect PerfMonV2 support")
Reported-by: Petr Tesarik <ptesarik@suse.com>
Closes: https://lore.kernel.org/all/20260717150315.2868314-1-ptesarik@suse.com/
Cc: stable@vger.kernel.org
Signed-off-by: Sandipan Das <sandipan.das@amd.com>
---
 arch/x86/events/amd/core.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index a787409f5a62..ecd648af81f7 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -841,6 +841,25 @@ static void amd_pmu_v2_disable_all(void)
 	amd_pmu_check_overflow();
 }
 
+static void amd_pmu_v2_print_debug(int cpu)
+{
+	u64 ctrl, status, debugextn;
+
+	rdmsrq(MSR_AMD64_PERF_CNTR_GLOBAL_CTL, ctrl);
+	rdmsrq(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS, status);
+
+	pr_info("\n");
+	pr_info("CPU#%d: ctrl:       %016llx\n", cpu, ctrl);
+	pr_info("CPU#%d: status:     %016llx\n", cpu, status);
+
+	if (cpu_feature_enabled(X86_FEATURE_AMD_LBR_V2)) {
+		rdmsrq(MSR_AMD_DBG_EXTN_CFG, debugextn);
+		pr_info("CPU#%d: debugextn:  %016llx\n", cpu, debugextn);
+	}
+
+	x86_pmu_print_debug(cpu);
+}
+
 DEFINE_STATIC_CALL_NULL(amd_pmu_branch_add, *x86_pmu.add);
 
 static void amd_pmu_add_event(struct perf_event *event)
@@ -1452,6 +1471,7 @@ static int __init amd_core_pmu_init(void)
 		x86_pmu.disable_all = amd_pmu_v2_disable_all;
 		x86_pmu.enable = amd_pmu_v2_enable_event;
 		x86_pmu.handle_irq = amd_pmu_v2_handle_irq;
+		x86_pmu.print_debug = amd_pmu_v2_print_debug;
 		static_call_update(amd_pmu_test_overflow, amd_pmu_test_overflow_status);
 	}
 
-- 
2.53.0

Re: [PATCH 3/3] perf/x86/amd: Implement x86_pmu::print_debug

[Petr Tesarik]

On Thu, 6 Aug 2026 15:33:28 +0530
Sandipan Das <sandipan.das@amd.com> wrote:

> Implement x86_pmu::print_debug for PerfMonV2 capable processors to dump
> MSR_AMD64_PERF_CNTR_GLOBAL_{CTL,STATUS}, plus MSR_AMD_DBG_EXTN_CFG if
> LBR Extension Version 2 is available. Chain into x86_pmu_print_debug()
> afterwards to dump the event selectors and counters.
> 
> MSR_AMD64_PERF_CNTR_GLOBAL_STATUS_{CLR,SET} are left out since they are
> write-only.
> 
> Fixes: 21d59e3e2c40 ("perf/x86/amd/core: Detect PerfMonV2 support")
> Reported-by: Petr Tesarik <ptesarik@suse.com>
> Closes: https://lore.kernel.org/all/20260717150315.2868314-1-ptesarik@suse.com/
> Cc: stable@vger.kernel.org
> Signed-off-by: Sandipan Das <sandipan.das@amd.com>

This works great on my system, no more unchecked MSR access errors, and
the logged values look correct. Feel free to add

Tested-by: Petr Tesarik <ptesarik@suse.com>

Thank you!

Petr T

> ---
>  arch/x86/events/amd/core.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index a787409f5a62..ecd648af81f7 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -841,6 +841,25 @@ static void amd_pmu_v2_disable_all(void)
>  	amd_pmu_check_overflow();
>  }
>  
> +static void amd_pmu_v2_print_debug(int cpu)
> +{
> +	u64 ctrl, status, debugextn;
> +
> +	rdmsrq(MSR_AMD64_PERF_CNTR_GLOBAL_CTL, ctrl);
> +	rdmsrq(MSR_AMD64_PERF_CNTR_GLOBAL_STATUS, status);
> +
> +	pr_info("\n");
> +	pr_info("CPU#%d: ctrl:       %016llx\n", cpu, ctrl);
> +	pr_info("CPU#%d: status:     %016llx\n", cpu, status);
> +
> +	if (cpu_feature_enabled(X86_FEATURE_AMD_LBR_V2)) {
> +		rdmsrq(MSR_AMD_DBG_EXTN_CFG, debugextn);
> +		pr_info("CPU#%d: debugextn:  %016llx\n", cpu, debugextn);
> +	}
> +
> +	x86_pmu_print_debug(cpu);
> +}
> +
>  DEFINE_STATIC_CALL_NULL(amd_pmu_branch_add, *x86_pmu.add);
>  
>  static void amd_pmu_add_event(struct perf_event *event)
> @@ -1452,6 +1471,7 @@ static int __init amd_core_pmu_init(void)
>  		x86_pmu.disable_all = amd_pmu_v2_disable_all;
>  		x86_pmu.enable = amd_pmu_v2_enable_event;
>  		x86_pmu.handle_irq = amd_pmu_v2_handle_irq;
> +		x86_pmu.print_debug = amd_pmu_v2_print_debug;
>  		static_call_update(amd_pmu_test_overflow, amd_pmu_test_overflow_status);
>  	}
>