[PATCH 1/3] ARM: errata: only handle ARM erratum #326103 on affected cores

[Will Deacon]

Erratum #326103 ("FSR write bit incorrect on a SWP to read-only memory")
only affects the ARM 1136 core prior to r1p0. The workaround
disassembles the faulting instruction to determine whether it was a read
or write access on all v6 cores.

An issue has been reported on the ARM 11MPCore whereby loading the
faulting instruction may happen in parallel with that page being
unmapped, resulting in a deadlock due to the lack of TLB broadcasting
in hardware:

http://lists.infradead.org/pipermail/linux-arm-kernel/2012-March/091561.html

This patch limits the workaround so that it is only used on affected
cores, which are known to be UP only. Other v6 cores can rely on the
FSR to indicate the access type correctly.

Signed-off-by: Will Deacon <will.deacon at arm.com>
---
 arch/arm/Kconfig        |    9 +++++++++
 arch/arm/mm/abort-ev6.S |   17 +++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index cf006d4..36586dba 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1186,6 +1186,15 @@ if !MMU
 source "arch/arm/Kconfig-nommu"
 endif
 
+config ARM_ERRATA_326103
+	bool "ARM errata: FSR write bit incorrect on a SWP to read-only memory"
+	depends on CPU_V6
+	help
+	  Executing a SWP instruction to read-only memory does not set bit 11
+	  of the FSR on the ARM 1136 prior to r1p0. This causes the kernel to
+	  treat the access as a read, preventing a COW from occurring and
+	  causing the faulting task to livelock.
+
 config ARM_ERRATA_411920
 	bool "ARM errata: Invalidation of the Instruction Cache operation can fail"
 	depends on CPU_V6 || CPU_V6K
diff --git a/arch/arm/mm/abort-ev6.S b/arch/arm/mm/abort-ev6.S
index ff1f7cc..8074199 100644
--- a/arch/arm/mm/abort-ev6.S
+++ b/arch/arm/mm/abort-ev6.S
@@ -26,18 +26,23 @@ ENTRY(v6_early_abort)
 	mrc	p15, 0, r1, c5, c0, 0		@ get FSR
 	mrc	p15, 0, r0, c6, c0, 0		@ get FAR
 /*
- * Faulty SWP instruction on 1136 doesn't set bit 11 in DFSR (erratum 326103).
- * The test below covers all the write situations, including Java bytecodes
+ * Faulty SWP instruction on 1136 doesn't set bit 11 in DFSR.
  */
-	bic	r1, r1, #1 << 11		@ clear bit 11 of FSR
+#ifdef CONFIG_ARM_ERRATA_326103
+	ldr	ip, =0x4107b36
+	mrc	p15, 0, r3, c0, c0, 0		@ get processor id
+	teq	ip, r3, lsr #4			@ r0 ARM1136?
+	bne	do_DataAbort
 	tst	r5, #PSR_J_BIT			@ Java?
+	tsteq	r5, #PSR_T_BIT			@ Thumb?
 	bne	do_DataAbort
-	do_thumb_abort fsr=r1, pc=r4, psr=r5, tmp=r3
-	ldreq	r3, [r4]			@ read aborted ARM instruction
+	bic	r1, r1, #1 << 11		@ clear bit 11 of FSR
+	ldr	r3, [r4]			@ read aborted ARM instruction
 #ifdef CONFIG_CPU_ENDIAN_BE8
-	reveq	r3, r3
+	rev	r3, r3
 #endif
 	do_ldrd_abort tmp=ip, insn=r3
 	tst	r3, #1 << 20			@ L = 0 -> write
 	orreq	r1, r1, #1 << 11		@ yes.
+#endif
 	b	do_DataAbort
-- 
1.7.4.1