linux-kernel - Re: [PATCH 1/3] powerpc: Emulation support for load/store instructions on LE

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Date:   Thu, 3 Nov 2016 15:57:27 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Anton Blanchard <anton@...ba.org>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, duwe@....de, ast@...nel.org,
        viro@...iv.linux.org.uk, chris@...troguy.com, oss@...error.net,
        paul.gortmaker@...driver.com, oohall@...il.com,
        aneesh.kumar@...ux.vnet.ibm.com, lsorense@...lub.uwaterloo.ca,
        bauerman@...ux.vnet.ibm.com, paulus@...ba.org,
        naveen.n.rao@...ux.vnet.ibm.com,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] powerpc: Emulation support for load/store
 instructions on LE



On Thursday 03 November 2016 03:18 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> writes:
>
>> On Thursday 03 November 2016 02:34 AM, Anton Blanchard wrote:
>>> Hi Ravi,
>>>
>>>> emulate_step() uses a number of underlying kernel functions that were
>>>> initially not enabled for LE. This has been rectified since. So, fix
>>>> emulate_step() for LE for the corresponding instructions.
>>> Thanks. Should this be queued up for stable?
>> Thanks Anton. Yes, this should go in stable.
> It's fairly big for stable. Does it fix an actual bug? If so what, and
> how bad is it, what's the user impact.

Hi Michael,

Yes, kernel-space hw-breakpoint feature is broken on LE without this.

Actually, there is no specific commit that introduced this. Back
in 2010, Paul Mackerras has added emulation support for load/store
instructions for BE. hw-breakpoint was also develpoed by K.Prasad
in the same timeframe.

Kernel-space hw-breakpoint emulates causative instruction before
notifying to user. As emulate_step is never enabled for LE, kernel-
space hw-breakpoint is always broken on LE.

-Ravi

> Can you also pinpoint which commit it "fixes"?
>
> cheers
>