Re: [perf] unchecked MSR access error: WRMSR to 0x3f1

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2025-06-17 11:39 a.m., Vince Weaver wrote:
> Hello
> 
> When running the perf_fuzzzer on a raptor-lake machine I get a
> 	unchecked MSR access error: WRMSR to 0x3f1
> error (see below).
> 
> A similar message happened before back in 2021 and was fixed in
> commit 2dc0572f2cef87425147658698dce2600b799bd3 so not sure if this is the 
> same problem or something new.

The commit 2dc0572f2cef was triggered by the fake event VLBR_EVENT.
But this error should be triggered by the Topdown perf metrics event,
INTEL_TD_METRIC_RETIRING, which uses the idx 48 internally.

We never support perf metrics events in sampling mode. The PEBS cannot
be enabled in counting mode. So it's weird the cpuc->pebs_enabled has
the idx 48 set.

The recent change I did for the PEBS is commit e02e9b0374c3
"perf/x86/intel: Support PEBS counters snapshotting". But it should not
impact the above.

Could you please help on the below questions?
- It only happens on the p-core, right?
- Which kernel base do you use? Is it 6.16-rc2?
- Can this be easily reproduced?
  Is it possible to bisect the error commit? (Maybe start from the
commit e02e9b0374c3?)

Thanks,
Kan>
> Vince Weaver
> vincent.weaver@maine.edu
> 
> [12646.001692] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0001000000000001) at rIP: 0xffffffffa98932af (native_write_msr+0xf/0x20)
> [12646.001698] Call Trace:
> [12646.001700]  <TASK>
> [12646.001700]  intel_pmu_pebs_enable_all+0x2c/0x40
> [12646.001703]  intel_pmu_enable_all+0xe/0x20
> [12646.001705]  ctx_resched+0x227/0x280
> [12646.001708]  event_function+0x8f/0xd0
> [12646.001710]  ? __pfx___perf_event_enable+0x10/0x10
> [12646.001711]  remote_function+0x42/0x50
> [12646.001713]  ? __pfx_remote_function+0x10/0x10
> [12646.001714]  generic_exec_single+0x6d/0x130
> [12646.001715]  smp_call_function_single+0xee/0x140
> [12646.001716]  ? __pfx_remote_function+0x10/0x10
> [12646.001717]  event_function_call+0x9f/0x1c0
> [12646.001718]  ? __pfx___perf_event_enable+0x10/0x10
> [12646.001720]  ? __pfx_event_function+0x10/0x10
> [12646.001721]  perf_event_task_enable+0x7b/0x100
> [12646.001723]  __do_sys_prctl+0x56f/0xca0
> [12646.001725]  do_syscall_64+0x84/0x2f0
> [12646.001727]  ? exit_to_user_mode_loop+0xcd/0x120
> [12646.001729]  ? do_syscall_64+0x1ef/0x2f0
> [12646.001730]  ? try_to_wake_up+0x7e/0x640
> [12646.001732]  ? complete_signal+0x2e8/0x350
> [12646.001734]  ? __send_signal_locked+0x2e3/0x450
> [12646.001735]  ? send_signal_locked+0xb6/0x120
> [12646.001736]  ? do_send_sig_info+0x6e/0xc0
> [12646.001737]  ? kill_pid_info_type+0xa6/0xc0
> [12646.001738]  ? kill_something_info+0x167/0x1a0
> [12646.001739]  ? syscall_exit_work+0x132/0x140
> [12646.001740]  ? do_syscall_64+0xbc/0x2f0
> [12646.001741]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [12646.001743] RIP: 0033:0x7efe86afd40d
> [12646.001744] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 18 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 9d 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 1b 48 8b 54 24 18 64 48 2b 14 25 28 00 00 00
> [12646.001745] RSP: 002b:00007ffcd6444cf0 EFLAGS: 00000246 ORIG_RAX: 000000000000009d
> [12646.001746] RAX: ffffffffffffffda RBX: 000000000000000e RCX: 00007efe86afd40d
> [12646.001747] RDX: 0000000000000001 RSI: 00007ffcd6444d24 RDI: 0000000000000020
> [12646.001747] RBP: 00007ffcd6444d60 R08: 00007efe86bc625c R09: 00007efe86bc6260
> [12646.001748] R10: 00007efe86bc6250 R11: 0000000000000246 R12: 0000000000000000
> [12646.001748] R13: 00007ffcd64471b8 R14: 0000559eb2a2edd8 R15: 00007efe86c30020
> [12646.001749]  </TASK>
>