[PATCH 3.4 32/45] ARM: 8129/1: errata: work around Cortex-A15 erratum 830321 using dummy strex

Zefan Li
2014-09-23T02:40:34Z

From: Mark Rutland <mark.rutland@arm.com>

3.4.104-rc1 review patch. If anyone has any objections, please let me know.

------------------

commit 2c32c65e3726c773760038910be30cce1b4d4149 upstream.

On revisions of Cortex-A15 prior to r3p3, a CLREX instruction at PL1 may
falsely trigger a watchpoint exception, leading to potential data aborts
during exception return and/or livelock.

This patch resolves the issue in the following ways:

- Replacing our uses of CLREX with a dummy STREX sequence instead (as
we did for v6 CPUs).

- Removing the clrex code from v7_exit_coherency_flush and derivatives,
since this only exists as a minor performance improvement when
non-cached exclusives are in use (Linux doesn't use these).

Benchmarking on a variety of ARM cores revealed no measurable
performance difference with this change applied, so the change is
performed unconditionally and no new Kconfig entry is added.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
[lizf: Backported to 3.4:
- Drop changes to arch/arm/include/asm/cacheflush.h and
arch/arm/mach-exynos/mcpm-exynos.c]
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
arch/arm/kernel/entry-header.S | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 9a8531e..9d95a46 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -76,26 +76,21 @@
#ifndef CONFIG_THUMB2_KERNEL
.macro svc_exit, rpsr
msr spsr_cxsf, \rpsr
-#if defined(CONFIG_CPU_V6)
- ldr r0, [sp]
- strex r1, r2, [sp] @ clear the exclusive monitor
- ldmib sp, {r1 - pc}^ @ load r1 - pc, cpsr
-#elif defined(CONFIG_CPU_32v6K)
- clrex @ clear the exclusive monitor
- ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
-#else
- ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
+#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
+ @ We must avoid clrex due to Cortex-A15 erratum #830321
+ sub r0, sp, #4 @ uninhabited address
+ strex r1, r2, [r0] @ clear the exclusive monitor
#endif
+ ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
.endm

.macro restore_user_regs, fast = 0, offset = 0
ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
ldr lr, [sp, #\offset + S_PC]! @ get pc
msr spsr_cxsf, r1 @ save in spsr_svc
-#if defined(CONFIG_CPU_V6)
+#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
+ @ We must avoid clrex due to Cortex-A15 erratum #830321
strex r1, r2, [sp] @ clear the exclusive monitor
-#elif defined(CONFIG_CPU_32v6K)
- clrex @ clear the exclusive monitor
#endif
.if \fast
ldmdb sp, {r1 - lr}^ @ get calling r1 - lr
@@ -123,7 +118,10 @@
.macro svc_exit, rpsr
ldr lr, [sp, #S_SP] @ top of the stack
ldrd r0, r1, [sp, #S_LR] @ calling lr and pc
- clrex @ clear the exclusive monitor
+
+ @ We must avoid clrex due to Cortex-A15 erratum #830321
+ strex r2, r1, [sp, #S_LR] @ clear the exclusive monitor
+
stmdb lr!, {r0, r1, \rpsr} @ calling lr and rfe context
ldmia sp, {r0 - r12}
mov sp, lr
@@ -132,13 +130,16 @@
.endm

.macro restore_user_regs, fast = 0, offset = 0
- clrex @ clear the exclusive monitor
mov r2, sp
load_user_sp_lr r2, r3, \offset + S_SP @ calling sp, lr
ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
ldr lr, [sp, #\offset + S_PC] @ get pc
add sp, sp, #\offset + S_SP
msr spsr_cxsf, r1 @ save in spsr_svc
+
+ @ We must avoid clrex due to Cortex-A15 erratum #830321
+ strex r1, r2, [sp] @ clear the exclusive monitor
+
.if \fast
ldmdb sp, {r1 - r12} @ get calling r1 - r12
.else
--
1.7.9.5