Re: [PATCH v8 12/14] x86: perf: intel_pt: Intel PT PMU driver

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

Peter Zijlstra <peterz@infradead.org> writes:

> On Fri, Nov 14, 2014 at 03:43:45PM +0200, Alexander Shishkin wrote:
>> +static __init int pt_init(void)
>> +{
>> +	int ret, cpu, prior_warn = 0;
>> +
>> +	BUILD_BUG_ON(sizeof(struct topa) > PAGE_SIZE);
>> +	get_online_cpus();
>> +	for_each_online_cpu(cpu) {
>> +		u64 ctl;
>> +
>> +		ret = rdmsrl_safe_on_cpu(cpu, MSR_IA32_RTIT_CTL, &ctl);
>> +		if (!ret && (ctl & RTIT_CTL_TRACEEN))
>> +			prior_warn++;
>> +	}
>> +	put_online_cpus();
>> +
>> +	ret = pt_pmu_hw_init();
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (!pt_cap_get(PT_CAP_topa_output)) {
>> +		pr_warn("ToPA output is not supported on this CPU\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	if (prior_warn)
>> +		pr_warn("PT is enabled at boot time, traces may be empty\n");
>
> Should we not also add_exclusive(pt) here?

Good point.

> Also, if its already enabled, should we not return ENODEV as well, no
> saying who or what programmed it, we should not be touching it.

Indeed we should, although I'd also like to have a force-override boot
time option for this.

Thanks,
--
Alex