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authorLeif Lindholm <leif.lindholm@arm.com>2010-09-16 18:00:47 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2010-11-04 15:45:24 +0000
commit64d2dc384e41e2b7acead6804593ddaaf8aad8e1 (patch)
tree07f6e34981bd4a6642cdffb546b32a2a973aec5d /arch/arm/mm
parent247055aa21ffef1c49dd64710d5e94c2aee19b58 (diff)
ARM: 6396/1: Add SWP/SWPB emulation for ARMv7 processors
The SWP instruction was deprecated in the ARMv6 architecture, superseded by the LDREX/STREX family of instructions for load-linked/store-conditional operations. The ARMv7 multiprocessing extensions mandate that SWP/SWPB instructions are treated as undefined from reset, with the ability to enable them through the System Control Register SW bit. This patch adds the alternative solution to emulate the SWP and SWPB instructions using LDREX/STREX sequences, and log statistics to /proc/cpu/swp_emulation. To correctly deal with copy-on-write, it also modifies cpu_v7_set_pte_ext to change the mappings to priviliged RO when user RO. Signed-off-by: Leif Lindholm <leif.lindholm@arm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Kirill A. Shutemov <kirill@shutemov.name> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r--arch/arm/mm/Kconfig27
-rw-r--r--arch/arm/mm/proc-v7.S4
2 files changed, 31 insertions, 0 deletions
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 6d05f79a8cd..8493ed04797 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -636,6 +636,33 @@ config ARM_THUMBEE
Say Y here if you have a CPU with the ThumbEE extension and code to
make use of it. Say N for code that can run on CPUs without ThumbEE.
+config SWP_EMULATE
+ bool "Emulate SWP/SWPB instructions"
+ depends on CPU_V7
+ select HAVE_PROC_CPU if PROC_FS
+ default y if SMP
+ help
+ ARMv6 architecture deprecates use of the SWP/SWPB instructions.
+ ARMv7 multiprocessing extensions introduce the ability to disable
+ these instructions, triggering an undefined instruction exception
+ when executed. Say Y here to enable software emulation of these
+ instructions for userspace (not kernel) using LDREX/STREX.
+ Also creates /proc/cpu/swp_emulation for statistics.
+
+ In some older versions of glibc [<=2.8] SWP is used during futex
+ trylock() operations with the assumption that the code will not
+ be preempted. This invalid assumption may be more likely to fail
+ with SWP emulation enabled, leading to deadlock of the user
+ application.
+
+ NOTE: when accessing uncached shared regions, LDREX/STREX rely
+ on an external transaction monitoring block called a global
+ monitor to maintain update atomicity. If your system does not
+ implement a global monitor, this option can cause programs that
+ perform SWP operations to uncached memory to deadlock.
+
+ If unsure, say Y.
+
config CPU_BIG_ENDIAN
bool "Build big-endian kernel"
depends on ARCH_SUPPORTS_BIG_ENDIAN
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index cfc11afab1f..2b5b20baf80 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -314,6 +314,10 @@ __v7_setup:
#ifdef CONFIG_CPU_ENDIAN_BE8
orr r6, r6, #1 << 25 @ big-endian page tables
#endif
+#ifdef CONFIG_SWP_EMULATE
+ orr r5, r5, #(1 << 10) @ set SW bit in "clear"
+ bic r6, r6, #(1 << 10) @ clear it in "mmuset"
+#endif
mrc p15, 0, r0, c1, c0, 0 @ read control register
bic r0, r0, r5 @ clear bits them
orr r0, r0, r6 @ set them