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

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Date:   Wed, 27 May 2020 12:59:35 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'kan.liang@...ux.intel.com'" <kan.liang@...ux.intel.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

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.

	David

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