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

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Message-ID: <9f0ed889-590e-6f7a-85bd-c4be43e993f3@linux.intel.com>
Date:   Wed, 27 May 2020 11:01:22 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] perf/x86/intel/uncore: Fix oops when counting IMC uncore
 events on some TGL



On 5/27/2020 10:51 AM, David Laight wrote:
> From: Liang, Kan
>> Sent: 27 May 2020 15:47
>> On 5/27/2020 8:59 AM, David Laight wrote:
>>> From: kan.liang@...ux.intel.com
>>>> Sent: 27 May 2020 13:31
>>>>
>>>> From: Kan Liang <kan.liang@...ux.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.
> 
> You need a check that the actual access is withing the mapped area.
> So instead of getting an OOPS you get a error.
> 
> This is after you've mapped it.

Sure. Will add a WARN_ONCE() before the actual access.

Thanks,
Kan

> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
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