Re: [PATCH 3/6] perf/x86/intel/pt: Stop tracing at syscore shutdown

[Adrian Hunter <adrian.hunter@intel.com>]

On 02/11/2026 18:15, Andi Kleen wrote:
>> +
>> +/*
>> + * Tracing must not continue into a kexec'ed kernel, which may reuse the
>> + * trace buffer memory, so stop tracing on all CPUs and prevent it from
>> + * being started again. Events are left in place, but record nothing more.
>> + */
>> +static void pt_syscore_shutdown(void *data)
>> +{
>> +	WRITE_ONCE(pt_shutdown, true);
>> +	on_each_cpu(pt_shutdown_cpu, NULL, 1);
> 
> I don't think adding more and more broadcast NMIs to the panic path 
> is a good idea. It's always a very big hammer and a risky operation
> that risks breaking the actual dump. panic reallhy needs to be
> simple and reliable, and this is the total opposite.

Is pt_syscore_shutdown() called on a panic path?  I can't find a way.

> 
> KVM already does one at least (which I never liked either). At a
> minimum please find a way to consolidate those into a single
> one (as in have a notifier chain that is called on the target CPU).
> 
> But better would be to not do this and find some other way.
> 
> How about just passing the PT region as reserved and maybe free
> it later after the target kernel had a chance to reinitialize all CPUs?

Intel PT has cpu_emergency_stop_pt().