Re: [PATCH] perf/x86/intel/uncore: Fix oops when counting IMC uncore events on some TGL

["Liang, Kan" <kan.liang@linux.intel.com>]

On 5/27/2020 8:59 AM, David Laight wrote:
> From: kan.liang@linux.intel.com
>> Sent: 27 May 2020 13:31
>>
>> From: Kan Liang <kan.liang@linux.intel.com>
>>
>> When counting IMC uncore events on some TGL machines, an oops will be
>> triggered.
>>    [ 393.101262] BUG: unable to handle page fault for address:
>>    ffffb45200e15858
>>    [ 393.101269] #PF: supervisor read access in kernel mode
>>    [ 393.101271] #PF: error_code(0x0000) - not-present page
>>
>> Current perf uncore driver still use the IMC MAP SIZE inherited from
>> SNB, which is 0x6000.
>> However, the offset of IMC uncore counters for some TGL machines is
>> larger than 0x6000, e.g. 0xd8a0.
>>
>> Enlarge the IMC MAP SIZE for TGL to 0xe000.
> 
> Replacing one 'random' constant with a different one
> doesn't seem like a proper fix.
> 
> Surely the actual bounds of the 'memory' area are properly
> defined somewhere.
> Or at least should come from a table.
> 
> You also need to verify that the offsets are within the mapped area.
> An unexpected offset shouldn't try to access an invalid address.

Thanks for the review.

I agree that we should add a check before mapping the area to prevent 
the issue happens again.

I think the check should be a generic check for all platforms which try 
to map an area, not just for TGL. I will submit a separate patch for the 
check.

Thanks,
Kan

> 
> 	David
> 
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