powerpc/64: Fix kernel stack 16-byte alignment

[Michael Ellerman]

On Thu, 2018-11-15 at 02:34:27 UTC, Nicholas Piggin wrote:
> Commit 4c2de74cc869 ("powerpc/64: Interrupts save PPR on stack rather
> than thread_struct") changed sizeof(struct pt_regs) % 16 from 0 to 8,
> which causes the interrupt frame allocation on kernel entry to put the
> kernel stack out of alignment.
> 
> Add a pad field to fix alignment, and add a BUILD_BUG_ON to catch this
> in future.
> 
> Fixes: 4c2de74cc869 ("powerpc/64: Interrupts save PPR on stack rather
> than thread_struct")
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/66f93c5a02d5ba6ef17fef45914396

cheers