diff mbox series

[v2] powerpc64/idle: Fix SP offsets when saving GPRs

Message ID 20210206072342.5067-1-cmr@codefail.de (mailing list archive)
State Accepted
Headers show
Series [v2] powerpc64/idle: Fix SP offsets when saving GPRs | expand

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snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (44158b256b30415079588d0fcb1bccbdc2ccd009)
snowpatch_ozlabs/build-ppc64le success Build succeeded
snowpatch_ozlabs/build-ppc64be success Build succeeded
snowpatch_ozlabs/build-ppc64e success Build succeeded
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snowpatch_ozlabs/needsstable success Patch has no Fixes tags

Commit Message

Christopher M. Riedl Feb. 6, 2021, 7:23 a.m. UTC 
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>
---
 arch/powerpc/kernel/idle_book3s.S | 138 ++++++++++++++++--------------
 1 file changed, 73 insertions(+), 65 deletions(-)

Comments

Michael Ellerman Feb. 10, 2021, 12:57 p.m. UTC | #1 
On Sat, 6 Feb 2021 01:23:42 -0600, Christopher M. Riedl wrote:
> 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.

Applied to powerpc/next.

[1/1] powerpc64/idle: Fix SP offsets when saving GPRs
      https://git.kernel.org/powerpc/c/73287caa9210ded6066833195f4335f7f688a46b

cheers
diff mbox series

Patch

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 22f249b6f58d..f9e6d83e6720 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -52,28 +52,32 @@  _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 */
@@ -89,8 +93,8 @@  _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
 	/*
@@ -98,25 +102,25 @@  _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
 
 /*
@@ -154,28 +158,32 @@  _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)