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powerpc/32: Preserve cr1 in exception prolog stack check to fix build error

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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: 98bf2d3f49 ("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.1612768623.git.christophe.leroy@csgroup.eu
This commit is contained in:
Christophe Leroy 2021-02-08 07:17:40 +00:00 committed by Michael Ellerman
parent ac7c5e9b08
commit 3642eb2125
2 changed files with 1 additions and 7 deletions
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2
arch/powerpc/kernel/head_32.h
View File

@ -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 */

6
arch/powerpc/kernel/head_book3s_32.S
View File

@ -269,12 +269,6 @@ 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