On Mon, May 8, 2017 at 9:55 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>
> Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.
>
> The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
> mode, due to the way it performs arithmetic on the program counter, so it
> is built in ARM mode instead. However, building C files in ARM mode under
> CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
> by subsystems like ftrace does not expect having to deal with interworking
> branches.
>
> Since the sequence in question is simply a poor man's ISB instruction,
> let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
> implies V7, so 'isb' should always be supported in that case.
>
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> Hi Greg,
>
> As Ard pointed out, commit 13d1b9575ac2c2da ("ARM: 8221/1: PJ4: allow
> building in Thumb-2 mode") which I suggested for backports into
> 3.16 is broken unless we also take this one.
>
> I checked the other stable branches and found that both 3.18 and
> 4.4 contain only the first of the two, so please apply this one on
> both branches as well.
Clarification: please apply this patch from email on 3.18.y and
cherry-pick the original 5008efc83bf85b6 on 4.4.y to avoid
rebasing yourself.
Arnd