linux-kernel - [PATCH v2 09/14] powerpc/32: Preserve cr1 in exception prolog stack check

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Date:   Fri, 22 Jan 2021 10:05:32 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v2 09/14] powerpc/32: Preserve cr1 in exception prolog stack
 check

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.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 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 1f5e64c70ddb..a7087930a844 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -55,7 +55,7 @@
 	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 */
diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 281de00c2ea4..6543cb410a8d 100644
--- 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
-- 
2.25.0