[PATCH 07/12] ARM: kernel: use relative references for UP/SMP alternatives

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-efi@vger.kernel.org
Cc: Nicolas Pitre <nico@fluxnic.net>, Marc Zyngier <maz@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	Stefan Agner <stefan@agner.ch>, Peter Smith <Peter.Smith@arm.com>,
	Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH 07/12] ARM: kernel: use relative references for UP/SMP alternatives
Date: Mon, 14 Sep 2020 12:57:01 +0300	[thread overview]
Message-ID: <20200914095706.3985-8-ardb@kernel.org> (raw)
In-Reply-To: <20200914095706.3985-1-ardb@kernel.org>

Currently, the .alt.smp.init section contains the virtual addresses
of the patch sites. Since patching may occur both before and after
switching into virtual mode, this requires some manual handling of
the address when applying the UP alternative.

Let's simplify this by using relative offsets in the table entries:
this allows us to simply add each entry's address to its contents,
regardless of whether we are running in virtual mode or not.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/include/asm/assembler.h |  4 ++--
 arch/arm/include/asm/processor.h |  2 +-
 arch/arm/kernel/head.S           | 10 +++++-----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 39e972eaaa3f..bf7501dfcb71 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -259,7 +259,7 @@
  */
 #define ALT_UP(instr...)					\
 	.pushsection ".alt.smp.init", "a"			;\
-	.long	9998b						;\
+	.long	9998b - .					;\
 9997:	instr							;\
 	.if . - 9997b == 2					;\
 		nop						;\
@@ -270,7 +270,7 @@
 	.popsection
 #define ALT_UP_B(label)					\
 	.pushsection ".alt.smp.init", "a"			;\
-	.long	9998b						;\
+	.long	9998b - .					;\
 	W(b)	. + (label - 9998b)					;\
 	.popsection
 #else
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index b9241051e5cb..9e6b97286307 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -96,7 +96,7 @@ unsigned long get_wchan(struct task_struct *p);
 #define __ALT_SMP_ASM(smp, up)						\
 	"9998:	" smp "\n"						\
 	"	.pushsection \".alt.smp.init\", \"a\"\n"		\
-	"	.long	9998b\n"					\
+	"	.long	9998b - .\n"					\
 	"	" up "\n"						\
 	"	.popsection\n"
 #else
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 40407a4727e0..3199d29f4480 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -546,14 +546,15 @@ smp_on_up:
 __do_fixup_smp_on_up:
 	cmp	r4, r5
 	reths	lr
-	ldmia	r4!, {r0, r6}
- ARM(	str	r6, [r0, r3]	)
- THUMB(	add	r0, r0, r3	)
+	ldmia	r4, {r0, r6}
+ ARM(	str	r6, [r0, r4]	)
+ THUMB(	add	r0, r0, r4	)
+	add	r4, r4, #8
 #ifdef __ARMEB__
  THUMB(	mov	r6, r6, ror #16	)	@ Convert word order for big-endian.
 #endif
  THUMB(	strh	r6, [r0], #2	)	@ For Thumb-2, store as two halfwords
- THUMB(	mov	r6, r6, lsr #16	)	@ to be robust against misaligned r3.
+ THUMB(	mov	r6, r6, lsr #16	)	@ to be robust against misaligned r0.
  THUMB(	strh	r6, [r0]	)
 	b	__do_fixup_smp_on_up
 ENDPROC(__do_fixup_smp_on_up)
@@ -562,7 +563,6 @@ ENTRY(fixup_smp)
 	stmfd	sp!, {r4 - r6, lr}
 	mov	r4, r0
 	add	r5, r0, r1
-	mov	r3, #0
 	bl	__do_fixup_smp_on_up
 	ldmfd	sp!, {r4 - r6, pc}
 ENDPROC(fixup_smp)
-- 
2.17.1


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