linux-kernel - Re: [PATCH v4 10/10] powerpc/watchpoint: Remove 512 byte boundary

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Date:   Tue, 21 Jul 2020 08:54:54 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Jordan Niethe <jniethe5@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>, mikey@...ling.org,
        apopple@...ux.ibm.com, Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, pedromfc@...ibm.com, miltonm@...ibm.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v4 10/10] powerpc/watchpoint: Remove 512 byte boundary

Hi Jordan,

On 7/20/20 12:24 PM, Jordan Niethe wrote:
> On Fri, Jul 17, 2020 at 2:11 PM Ravi Bangoria
> <ravi.bangoria@...ux.ibm.com> wrote:
>>
>> Power10 has removed 512 bytes boundary from match criteria. i.e. The watch
>> range can cross 512 bytes boundary.
> It looks like this change is not mentioned in ISA v3.1 Book III 9.4
> Data Address Watchpoint. It could be useful to mention that in the
> commit message.

Yes, ISA 3.1 Book III 9.4 has a documentation mistake and hopefully it
will be fixed in the next version of ISA. Though, this is mentioned in
ISA 3.1 change log:

   Multiple DEAW:
   Added a second Data Address Watchpoint. [H]DAR is
   set to the first byte of overlap. 512B boundary is
   removed.

I'll mention this in the commit description.

> Also I wonder if could add a test for this to the ptrace-hwbreak selftest?

Yes, I already have a selftest for this in perf-hwbreak. Will send that soon.

Thanks,
Ravi