This is backport of 3642eb21256a ("powerpc/32: Preserve cr1 in exception prolog stack check to fix build error") for kernel 5.10

It fixes the build failure on v5.10 reported by kernel test robot and by David Michael.

This fix is not in Linux tree yet, it is in next branch in powerpc tree.

(cherry picked from commit 3642eb21256a317ac14e9ed560242c6d20cf06d9)

THREAD_ALIGN_SHIFT = THREAD_SHIFT + 1 = PAGE_SHIFT + 1 Maximum PAGE_SHIFT is 18 for 256k pages so THREAD_ALIGN_SHIFT is 19 at the maximum.

No need to clobber cr1, it can be preserved when moving r1 into CR when we check stack overflow.

This reduces the number of instructions in Machine Check Exception prolog and fixes a build failure reported by the kernel test robot on v5.10 stable when building with RTAS + VMAP_STACK + KVM. That build failure is due to too many instructions in the prolog hence not fitting between 0x200 and 0x300. Allthough the problem doesn't show up in mainline, it is still worth the change.

Fixes: 98bf2d3f4970 ("powerpc/32s: Fix RTAS machine check with VMAP stack") Cc: stable@vger.kernel.org Reported-by: kernel test robot lkp@intel.com Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/5ae4d545e3ac58e133d2599e0deb88843cb494fc.161276862... --- arch/powerpc/kernel/head_32.h | 2 +- arch/powerpc/kernel/head_book3s_32.S | 6 ------ 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h index c88e66adecb5..fef0b34a77c9 100644 --- a/arch/powerpc/kernel/head_32.h +++ b/arch/powerpc/kernel/head_32.h @@ -56,7 +56,7 @@ 1: tophys_novmstack r11, r11 #ifdef CONFIG_VMAP_STACK - mtcrf 0x7f, r1 + mtcrf 0x3f, r1 bt 32 - THREAD_ALIGN_SHIFT, stack_overflow #endif .endm diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S index d66da35f2e8d..2729d8fa6e77 100644 --- a/arch/powerpc/kernel/head_book3s_32.S +++ b/arch/powerpc/kernel/head_book3s_32.S @@ -280,12 +280,6 @@ MachineCheck: 7: EXCEPTION_PROLOG_2 addi r3,r1,STACK_FRAME_OVERHEAD #ifdef CONFIG_PPC_CHRP -#ifdef CONFIG_VMAP_STACK - mfspr r4, SPRN_SPRG_THREAD - tovirt(r4, r4) - lwz r4, RTAS_SP(r4) - cmpwi cr1, r4, 0 -#endif beq cr1, machine_check_tramp twi 31, 0, 0 #else