This is backport for 5.10
(cherry picked from commit 98bf2d3f4970179c702ef64db658e0553bc6ef3a)
When we have VMAP stack, exception prolog 1 sets r1, not r11.
When it is not an RTAS machine check, don't trash r1 because it is
needed by prolog 1.
Fixes: da7bb43ab9da ("powerpc/32: Fix vmap stack - Properly set r1 before activating MMU")
Cc: stable@xxxxxxxxxxxxxxx # v5.10+
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
[mpe: Squash in fixup for RTAS machine check from Christophe]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/bc77d61d1c18940e456a2dee464f1e2eda65a3f0.1608621048.git.christophe.leroy@xxxxxxxxxx