Re: [PATCH] arch/x86: Fix kdump on x86 with physically hotadded CPUs

Prarit Bhargava
2016-10-06T15:25:55Z

On 10/05/2016 12:14 PM, Jiri Olsa wrote:
> On Tue, Oct 04, 2016 at 04:38:16PM +0200, Thomas Gleixner wrote:
>> On Tue, 4 Oct 2016, Prarit Bhargava wrote:
>>> On 10/04/2016 06:58 AM, Thomas Gleixner wrote:
>>>> While it is the right thing to initialize the package map in that case, it
>>>> still papers over a robustness issue in the uncore code, which needs to be
>>>> fixed first.
>>>
>>> I will include a separate patch with an error check for pkg == 0xffff in the
>>> uncore code.
>>
>> 0xffff? That won't help. The id returned is -1 if the entry is not
>> initialized. And aside of that just patching that particular place is not
>> helping as the uncore code and also rapl is relying on the package map
>> being populated.
>>
>> So we need a sanity check in the initialization code which prevents any of
>> this being executed.
>
> I still need to test this, but how about something like this?
>
> thanks,
> jirka
>
>
> ---
> diff --git a/arch/x86/events/intel/rapl.c b/arch/x86/events/intel/rapl.c
> index 28865938aadf..61d087a2f25d 100644
> --- a/arch/x86/events/intel/rapl.c
> +++ b/arch/x86/events/intel/rapl.c
> @@ -598,8 +598,13 @@ static int rapl_cpu_online(unsigned int cpu)
>
> static int rapl_cpu_prepare(unsigned int cpu)
> {
> - struct rapl_pmu *pmu = cpu_to_rapl_pmu(cpu);
> + struct rapl_pmu *pmu;
> + int pkg = topology_logical_package_id(cpu);
> +
> + if (WARN_ON(pkg == -1))
> + return -EINVAL;
>
> + pmu = cpu_to_rapl_pmu(cpu);
> if (pmu)
> return 0;

I thought about doing this but it seems like every time some driver uses
topology_logical_package_id() the driver would have to replicate the error
checking code.

P.