From: Kan Liang kan.liang@linux.intel.com

The below error can be observed in a Linux guest, when the hypervisor is on a hybrid machine.

[ 0.118214] unchecked MSR access error: WRMSR to 0x38f (tried to write 0x00011000f0000003f) at rIP: 0xffffffff83082124 (native_write_msr+0x4/0x30) [ 0.118949] Call Trace: [ 0.119092] <TASK> [ 0.119215] ? __intel_pmu_enable_all.constprop.0+0x88/0xe0 [ 0.119533] intel_pmu_enable_all+0x15/0x20 [ 0.119778] x86_pmu_enable+0x17c/0x320

The current perf wrongly assumes that the perf metrics feature is always enabled on p-core. It unconditionally enables the feature to workaround the unreliable enumeration of the PERF_CAPABILITIES MSR. The assumption is safe to bare metal. However, KVM doesn't support the perf metrics feature yet. Setting the corresponding bit triggers MSR access error in a guest.

Only unconditionally enable the core specific PMU feature for bare metal on ADL and RPL, which includes the perf metrics on p-core and PEBS-via-PT on e-core. For the future platforms, perf doesn't need to hardcode the PMU feature. The per-core PMU features can be enumerated by the enhanced PERF_CAPABILITIES MSR and CPUID leaf 0x23. There is no such issue.

Fixes: f83d2f91d259 ("perf/x86/intel: Add Alder Lake Hybrid support") Link: https://lore.kernel.org/lkml/e161b7c0-f0be-23c8-9a25-002260c2a085@linux.inte... Reported-by: Pengfei Xu pengfei.xu@intel.com Signed-off-by: Kan Liang kan.liang@linux.intel.com Cc: stable@vger.kernel.org ---

Based on my limit knowledge regarding KVM and guest, I use the HYPERVISOR bit to tell whether it's a guest. But I'm not sure whether it's reliable. Please let me know if there is a better way. Thanks.

arch/x86/events/intel/core.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index bbb7846d3c1e..8d08929a7250 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -6459,8 +6459,17 @@ __init int intel_pmu_init(void) __EVENT_CONSTRAINT(0, (1ULL << pmu->num_counters) - 1, 0, pmu->num_counters, 0, 0); pmu->intel_cap.capabilities = x86_pmu.intel_cap.capabilities; - pmu->intel_cap.perf_metrics = 1; - pmu->intel_cap.pebs_output_pt_available = 0; + /* + * The capability bits are not reliable on ADL and RPL. + * For bare metal, it's safe to assume that some features + * are always enabled, e.g., the perf metrics on p-core, + * but we cannot do the same assumption for a hypervisor. + * Only update the core specific PMU feature for bare metal. + */ + if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) { + pmu->intel_cap.perf_metrics = 1; + pmu->intel_cap.pebs_output_pt_available = 0; + }

memcpy(pmu->hw_cache_event_ids, spr_hw_cache_event_ids, sizeof(pmu->hw_cache_event_ids)); memcpy(pmu->hw_cache_extra_regs, spr_hw_cache_extra_regs, sizeof(pmu->hw_cache_extra_regs)); @@ -6480,8 +6489,10 @@ __init int intel_pmu_init(void) __EVENT_CONSTRAINT(0, (1ULL << pmu->num_counters) - 1, 0, pmu->num_counters, 0, 0); pmu->intel_cap.capabilities = x86_pmu.intel_cap.capabilities; - pmu->intel_cap.perf_metrics = 0; - pmu->intel_cap.pebs_output_pt_available = 1; + if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) { + pmu->intel_cap.perf_metrics = 0; + pmu->intel_cap.pebs_output_pt_available = 1; + }

memcpy(pmu->hw_cache_event_ids, glp_hw_cache_event_ids, sizeof(pmu->hw_cache_event_ids)); memcpy(pmu->hw_cache_extra_regs, tnt_hw_cache_extra_regs, sizeof(pmu->hw_cache_extra_regs));