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

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Date:   Thu, 06 Oct 2016 11:25:43 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     Jiri Olsa <jolsa@...hat.com>, Thomas Gleixner <tglx@...utronix.de>
CC:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
        Andi Kleen <ak@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>, dyoung@...hat.com,
        Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org
Subject: Re: [PATCH] arch/x86: Fix kdump on x86 with physically hotadded CPUs



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.