powerpc/64s: Fix hypercall entry clobbering r12 input

[Michael Ellerman]

On Tue, 2017-07-18 at 05:32:44 UTC, Nicholas Piggin wrote:
> A previous optimisation incorrectly assumed the PAPR hcall does
> not use r12, and clobbers it upon entry. In fact it is used as
> an input. This can result in KVM guests crashing (observed with
> PR KVM).
> 
> Instead of using r12 to save r13, tihs patch saves r13 in ctr.
> This is more costly, but not as slow as using the SPRG.
> 
> Fixes: acd7d8cef0153 ("powerpc/64s: Optimize hypercall/syscall entry")
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/76fc0cfcc5b0f520062ca6d7225b22

cheers