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 [off-list ref] writes:

quoted

On Thursday 03 November 2016 02:34 AM, Anton Blanchard wrote:

quoted

Hi Ravi,

quoted

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