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

From: Prarit Bhargava <prarit@redhat.com>
To: Jiri Olsa <jolsa@redhat.com>, Thomas Gleixner <tglx@linutronix.de>
Cc: Juergen Gross <jgross@suse.com>, Len Brown <len.brown@intel.com>,
	Andi Kleen <ak@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@suse.de>,
	dyoung@redhat.com
Subject: Re: [PATCH] arch/x86: Fix kdump on x86 with physically hotadded CPUs
Date: Thu, 06 Oct 2016 11:25:43 -0400	[thread overview]
Message-ID: <57F66CF7.7040204@redhat.com> (raw)
In-Reply-To: <20161005161455.GA26029@krava>

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.

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