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

From: Ravi Bangoria
Date: Thu Nov 03 2016 - 06:27:46 EST

On Thursday 03 November 2016 03:18 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> 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.


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