[perf] perf_fuzzer causes unchecked MSR access error

[Vince Weaver]

Hello

on my Haswell machine the perf_fuzzer managed to trigger this message:

[117248.075892] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0400000000000000) at rIP: 0xffffffff8106e4f4 (native_write_msr+0x4/0x20)
[117248.089957] Call Trace:
[117248.092685]  intel_pmu_pebs_enable_all+0x31/0x40
[117248.097737]  intel_pmu_enable_all+0xa/0x10
[117248.102210]  __perf_event_task_sched_in+0x2df/0x2f0
[117248.107511]  finish_task_switch.isra.0+0x15f/0x280
[117248.112765]  schedule_tail+0xc/0x40
[117248.116562]  ret_from_fork+0x8/0x30

that shouldn't be possible, should it?  MSR 0x3f1 is MSR_IA32_PEBS_ENABLE

this is on recent-git with the patch causing the pebs-related crash 
reverted.

Vince