Re: [PATCH] perf/x86/amd: check event before enable to avoid GPF

[Ravi Bangoria]

Hi George,

> Events can be deleted and the entry can be NULL.

Can you please also explain "how".

> 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?

> @@ -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])?

Thanks,
Ravi