linux-kernel - Re: [PATCH v3 2/3] Powerpc64/Watchpoint: Don't ignore extraneous exceptions

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Message-Id: <a49ccbd5-8109-b46e-66a3-c8deda841490@linux.ibm.com>
Date:   Wed, 10 Jul 2019 12:08:36 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     mpe@...erman.id.au, mikey@...ling.org, benh@...nel.crashing.org,
        paulus@...ba.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, npiggin@...il.com,
        naveen.n.rao@...ux.vnet.ibm.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v3 2/3] Powerpc64/Watchpoint: Don't ignore extraneous
 exceptions


On 7/10/19 11:57 AM, Christophe Leroy wrote:
> 
> 
> Le 10/07/2019 à 06:54, Ravi Bangoria a écrit :
>> On Powerpc64, watchpoint match range is double-word granular. On
>> a watchpoint hit, DAR is set to the first byte of overlap between
>> actual access and watched range. And thus it's quite possible that
>> DAR does not point inside user specified range. Ex, say user creates
>> a watchpoint with address range 0x1004 to 0x1007. So hw would be
>> configured to watch from 0x1000 to 0x1007. If there is a 4 byte
>> access from 0x1002 to 0x1005, DAR will point to 0x1002 and thus
>> interrupt handler considers it as extraneous, but it's actually not,
>> because part of the access belongs to what user has asked. So, let
>> kernel pass it on to user and let user decide what to do with it
>> instead of silently ignoring it. The drawback is, it can generate
>> false positive events.
> 
> Why adding some #ifdefs based on CONFIG_8xx ?

I don't know how 8xx behaves so I'm keeping the current behavior(ignore
extraneous exception) for 8xx.

> 
> I see your commit log mentions 'Powerpc64'. What about BOOK3S/32 ?

Hmm, I should not have mention 64 there. Yes, the change should cover both
Books3S/64 and Book3S/32.