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From:   Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Subject: Re: [PATCH v3 2/3] Powerpc64/Watchpoint: Don't ignore extraneous
 exceptions
To:     "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        mpe@ellerman.id.au
Cc:     mikey@neuling.org, benh@kernel.crashing.org,
        christophe.leroy@c-s.fr, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, paulus@samba.org,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>
References: <20190710045445.31037-1-ravi.bangoria@linux.ibm.com>
 <20190710045445.31037-3-ravi.bangoria@linux.ibm.com>
 <1567608022.j44gajn34z.naveen@linux.ibm.com>
Date:   Thu, 5 Sep 2019 09:26:44 +0530
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On 9/4/19 8:12 PM, Naveen N. Rao wrote:
> Ravi Bangoria wrote:
>> 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.
> 
> I think you should do the additional validation here, instead of generating false positives. You should be able to read the instruction, run it through analyse_instr(), and then use OP_IS_LOAD_STORE() and GETSIZE() to understand the access range. This can be used to then perform a better match against what the user asked for.

Ok. Let me see how feasible that is.

But patch 1 and 3 are independent of this and can still go in. mpe?

-Ravi