[PATCH 5.4 35/58] powerpc64/idle: Fix SP offsets when saving GPRs

Greg Kroah-Hartman
2021-10-25T19:40:05Z

From: Christopher M. Riedl <cmr@codefail.de>

commit 73287caa9210ded6066833195f4335f7f688a46b upstream.

The idle entry/exit code saves/restores GPRs in the stack "red zone"
(Protected Zone according to PowerPC64 ELF ABI v2). However, the offset
used for the first GPR is incorrect and overwrites the back chain - the
Protected Zone actually starts below the current SP. In practice this is
probably not an issue, but it's still incorrect so fix it.

Also expand the comments to explain why using the stack "red zone"
instead of creating a new stackframe is appropriate here.

Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210206072342.5067-1-cmr@codefail.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/kernel/idle_book3s.S | 138 ++++++++++++++++++++------------------
1 file changed, 73 insertions(+), 65 deletions(-)

--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -50,28 +50,32 @@ _GLOBAL(isa300_idle_stop_mayloss)
std r1,PACAR1(r13)
mflr r4
mfcr r5
- /* use stack red zone rather than a new frame for saving regs */
- std r2,-8*0(r1)
- std r14,-8*1(r1)
- std r15,-8*2(r1)
- std r16,-8*3(r1)
- std r17,-8*4(r1)
- std r18,-8*5(r1)
- std r19,-8*6(r1)
- std r20,-8*7(r1)
- std r21,-8*8(r1)
- std r22,-8*9(r1)
- std r23,-8*10(r1)
- std r24,-8*11(r1)
- std r25,-8*12(r1)
- std r26,-8*13(r1)
- std r27,-8*14(r1)
- std r28,-8*15(r1)
- std r29,-8*16(r1)
- std r30,-8*17(r1)
- std r31,-8*18(r1)
- std r4,-8*19(r1)
- std r5,-8*20(r1)
+ /*
+ * Use the stack red zone rather than a new frame for saving regs since
+ * in the case of no GPR loss the wakeup code branches directly back to
+ * the caller without deallocating the stack frame first.
+ */
+ std r2,-8*1(r1)
+ std r14,-8*2(r1)
+ std r15,-8*3(r1)
+ std r16,-8*4(r1)
+ std r17,-8*5(r1)
+ std r18,-8*6(r1)
+ std r19,-8*7(r1)
+ std r20,-8*8(r1)
+ std r21,-8*9(r1)
+ std r22,-8*10(r1)
+ std r23,-8*11(r1)
+ std r24,-8*12(r1)
+ std r25,-8*13(r1)
+ std r26,-8*14(r1)
+ std r27,-8*15(r1)
+ std r28,-8*16(r1)
+ std r29,-8*17(r1)
+ std r30,-8*18(r1)
+ std r31,-8*19(r1)
+ std r4,-8*20(r1)
+ std r5,-8*21(r1)
/* 168 bytes */
PPC_STOP
b . /* catch bugs */
@@ -87,8 +91,8 @@ _GLOBAL(isa300_idle_stop_mayloss)
*/
_GLOBAL(idle_return_gpr_loss)
ld r1,PACAR1(r13)
- ld r4,-8*19(r1)
- ld r5,-8*20(r1)
+ ld r4,-8*20(r1)
+ ld r5,-8*21(r1)
mtlr r4
mtcr r5
/*
@@ -96,25 +100,25 @@ _GLOBAL(idle_return_gpr_loss)
* from PACATOC. This could be avoided for that less common case
* if KVM saved its r2.
*/
- ld r2,-8*0(r1)
- ld r14,-8*1(r1)
- ld r15,-8*2(r1)
- ld r16,-8*3(r1)
- ld r17,-8*4(r1)
- ld r18,-8*5(r1)
- ld r19,-8*6(r1)
- ld r20,-8*7(r1)
- ld r21,-8*8(r1)
- ld r22,-8*9(r1)
- ld r23,-8*10(r1)
- ld r24,-8*11(r1)
- ld r25,-8*12(r1)
- ld r26,-8*13(r1)
- ld r27,-8*14(r1)
- ld r28,-8*15(r1)
- ld r29,-8*16(r1)
- ld r30,-8*17(r1)
- ld r31,-8*18(r1)
+ ld r2,-8*1(r1)
+ ld r14,-8*2(r1)
+ ld r15,-8*3(r1)
+ ld r16,-8*4(r1)
+ ld r17,-8*5(r1)
+ ld r18,-8*6(r1)
+ ld r19,-8*7(r1)
+ ld r20,-8*8(r1)
+ ld r21,-8*9(r1)
+ ld r22,-8*10(r1)
+ ld r23,-8*11(r1)
+ ld r24,-8*12(r1)
+ ld r25,-8*13(r1)
+ ld r26,-8*14(r1)
+ ld r27,-8*15(r1)
+ ld r28,-8*16(r1)
+ ld r29,-8*17(r1)
+ ld r30,-8*18(r1)
+ ld r31,-8*19(r1)
blr

/*
@@ -152,28 +156,32 @@ _GLOBAL(isa206_idle_insn_mayloss)
std r1,PACAR1(r13)
mflr r4
mfcr r5
- /* use stack red zone rather than a new frame for saving regs */
- std r2,-8*0(r1)
- std r14,-8*1(r1)
- std r15,-8*2(r1)
- std r16,-8*3(r1)
- std r17,-8*4(r1)
- std r18,-8*5(r1)
- std r19,-8*6(r1)
- std r20,-8*7(r1)
- std r21,-8*8(r1)
- std r22,-8*9(r1)
- std r23,-8*10(r1)
- std r24,-8*11(r1)
- std r25,-8*12(r1)
- std r26,-8*13(r1)
- std r27,-8*14(r1)
- std r28,-8*15(r1)
- std r29,-8*16(r1)
- std r30,-8*17(r1)
- std r31,-8*18(r1)
- std r4,-8*19(r1)
- std r5,-8*20(r1)
+ /*
+ * Use the stack red zone rather than a new frame for saving regs since
+ * in the case of no GPR loss the wakeup code branches directly back to
+ * the caller without deallocating the stack frame first.
+ */
+ std r2,-8*1(r1)
+ std r14,-8*2(r1)
+ std r15,-8*3(r1)
+ std r16,-8*4(r1)
+ std r17,-8*5(r1)
+ std r18,-8*6(r1)
+ std r19,-8*7(r1)
+ std r20,-8*8(r1)
+ std r21,-8*9(r1)
+ std r22,-8*10(r1)
+ std r23,-8*11(r1)
+ std r24,-8*12(r1)
+ std r25,-8*13(r1)
+ std r26,-8*14(r1)
+ std r27,-8*15(r1)
+ std r28,-8*16(r1)
+ std r29,-8*17(r1)
+ std r30,-8*18(r1)
+ std r31,-8*19(r1)
+ std r4,-8*20(r1)
+ std r5,-8*21(r1)
cmpwi r3,PNV_THREAD_NAP
bne 1f
IDLE_STATE_ENTER_SEQ_NORET(PPC_NAP)