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X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 51Uhyt5lc4YpQ6TSa8Ec8OCB3Tt1sHf7O7PjeXjPR0pB3kHa3TqluLwjINEN2+pDH2elL3jxDR3MZOcsf+VdKdUkjkXSEvkd1JRndW/jF4w= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR10MB6163 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-07-02_07,2024-07-02_02,2024-05-17_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 spamscore=0 mlxscore=0 adultscore=0 bulkscore=0 malwarescore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2406180000 definitions=main-2407020086 X-Proofpoint-GUID: ubEyAoReG2H7m12_q25d5g3L-KpB-Y4g X-Proofpoint-ORIG-GUID: ubEyAoReG2H7m12_q25d5g3L-KpB-Y4g On 7/2/2024 12:03 AM, Ravi Bangoria wrote: > On 24-Jun-24 9:48 PM, George Kennedy wrote: >> >> On 6/10/2024 6:51 AM, Ravi Bangoria wrote: >>> On 6/8/2024 12:43 AM, George Kennedy wrote: >>>> Hi Ravi, >>>> >>>> On 6/4/2024 9:40 AM, Ravi Bangoria wrote: >>>>>> On 6/4/2024 9:16 AM, Ravi Bangoria wrote: >>>>>>>>>>> Events can be deleted and the entry can be NULL. >>>>>>>>>> Can you please also explain "how". >>>>>>>>> It looks like x86_pmu_stop() is clearing the bit in active_mask and setting the events entry to NULL (and doing it in the correct order) for the same events index that amd_pmu_enable_all() is trying to enable. >>>>>>>>>>> Check event for NULL in amd_pmu_enable_all() before enable to avoid a GPF. >>>>>>>>>>> This appears to be an AMD only issue. >>>>>>>>>>> >>>>>>>>>>> Syzkaller reported a GPF in amd_pmu_enable_all. >>>>>>>>>> Can you please provide a bug report link? Also, any reproducer? >>>>>>>>> The Syzkaller reproducer can be found in this link: >>>>>>>>> https://lore.kernel.org/netdev/CAMt6jhyec7-TSFpr3F+_ikjpu39WV3jnCBBGwpzpBrPx55w20g@mail.gmail.com/T/#u >>>>>>>>>>> @@ -760,7 +760,8 @@ static void amd_pmu_enable_all(int added) >>>>>>>>>>>              if (!test_bit(idx, cpuc->active_mask)) >>>>>>>>>>>                  continue; >>>>>>>>>>>      -        amd_pmu_enable_event(cpuc->events[idx]); >>>>>>>>>>> +        if (cpuc->events[idx]) >>>>>>>>>>> +            amd_pmu_enable_event(cpuc->events[idx]); >>>>>>>>>> What if cpuc->events[idx] becomes NULL after if (cpuc->events[idx]) but >>>>>>>>>> before amd_pmu_enable_event(cpuc->events[idx])? >>>>>>>>> Good question, but the crash has not reproduced with the proposed fix in hours of testing. It usually reproduces within minutes without the fix. >>>>>>>> Also, a similar fix is done in __intel_pmu_enable_all() in arch/x86/events/intel/core.c except that a WARN_ON_ONCE is done as well. >>>>>>>> See: https://elixir.bootlin.com/linux/v6.10-rc1/source/arch/x86/events/intel/core.c#L2256 >>>>>>> There are subtle differences between Intel and AMD pmu implementation. >>>>>>> __intel_pmu_enable_all() enables all event with single WRMSR whereas >>>>>>> amd_pmu_enable_all() loops over each PMC and enables it individually. >>>>>>> >>>>>>> The WARN_ON_ONCE() is important because it will warn about potential >>>>>>> sw bug somewhere else. >>>>>> We could add a similar WARN_ON_ONCE() to the proposed patch. >>>>> Sure, that would help in future. But for current splat, can you please >>>>> try to rootcause the underlying race condition? >>>> Were you able to reproduce the crash on the AMD machine? >>> I'm able to reproduce within the KVM guest. Will try to investigate further. >> Hi Ravi, >> >> Any new status? > I was able to reproduce it with passthrough pmu[1] as well on a Zen4 machine > where Host has PerfMonV2 support (GlobalCtrl etc) but guest do not. I've > debugged it at some extent and seeing some race conditions, but not working > on this with top priority since this requires root/CAP_PERFMON privileges to > cause a crash. I'll resume investigation once I get some time. Sorry about > the delay. No worries. Thank you for the update, Ravi, George > > [1] https://lore.kernel.org/all/20240506053020.3911940-1-mizhang@google.com > > Thanks, > Ravi