[PATCH] powerpc/kexec: Fix radix to hash kexec

[Michael Ellerman]

Balbir Singh <bsingharora at gmail.com> writes:

> This patch fixes a crash seen while doing a kexec from
> radix mode to hash mode. Key 0 is special in hash and
> used in the RPN by default, we set the key values to 0
> today. In radix mode key 0 is used to control
> supervisor<->user access. In hash key 0 is used by default,
> so the first instruction after the switch causes a crash on
> kexec.
>
> This patch fixes
> (3b10d00 powerpc/mm/radix: Prevent kernel execution of user space)
> The commit above introduced setting of IAMR and AMOR values to
> prevent execution of user mode instructions from supervisor mode.
> We need to clean up these SPR's on kexec.
>
> Reported-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Signed-off-by: Balbir Singh <bsingharora at gmail.com>
> ---
>
> NOTES:
>  This patch can be made power9 specific, but I've chosen not
>  to do so, I could add it in a feature section if recommended.

Well neither register existed in the architecture prior to Power8.
Possibly they were defined in BookIV or they were nops, but most likely
it will just explode on old CPUs.

And probably Book3E as well.

So it should be in a CPU_FTR_ARCH_207S section at a minimum.

But maybe it should just be done in C earlier in the call chain.

cheers