From: Christophe Leroy christophe.leroy@csgroup.eu
commit 3642eb21256a317ac14e9ed560242c6d20cf06d9 upstream.
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... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/kernel/head_32.h | 2 +- arch/powerpc/kernel/head_book3s_32.S | 6 ------ 2 files changed, 1 insertion(+), 7 deletions(-)
--- a/arch/powerpc/kernel/head_32.h +++ b/arch/powerpc/kernel/head_32.h @@ -47,7 +47,7 @@ lwz r1,TASK_STACK-THREAD(r1) addi r1, r1, THREAD_SIZE - INT_FRAME_SIZE 1: - mtcrf 0x7f, r1 + mtcrf 0x3f, r1 bt 32 - THREAD_ALIGN_SHIFT, stack_overflow #else subi r11, r1, INT_FRAME_SIZE /* use r1 if kernel */ --- a/arch/powerpc/kernel/head_book3s_32.S +++ b/arch/powerpc/kernel/head_book3s_32.S @@ -278,12 +278,6 @@ 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