diff options
Diffstat (limited to 'arch/arm/mm')
| -rw-r--r-- | arch/arm/mm/Kconfig | 27 | ||||
| -rw-r--r-- | arch/arm/mm/proc-v7.S | 4 |
2 files changed, 31 insertions, 0 deletions
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig index 6d05f79a8cd2..8493ed04797a 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 cfc11afab1fb..2b5b20baf80d 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 |