ARM: SWP emulation: always enable when SMP is enabled

SWP is deprecated in ARMv6 and ARMv7 CPUs, but more importantly, when
running on a SMP system, SWP doesn't guarantee atomicity.  This means
it can't really be used (by userspace) for locking purposes in a SMP
environment.

Currently, many configurations leave the SWP emulation disabled, which
means we never know if userspace executes this instruction on ARMv7
hardware.  Rectify this by enabling SWP emulation for ARMv7 with SMP
(where we can trap the instruction.)

Tested-by: Tony Lindgren <tony@atomide.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index c348eaee7ee29df402ce9103a94174cbb1883213..c78c7db6aa8307124815bdd64476e0a1b1553dde 100644 (file)
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -669,7 +669,7 @@ config ARM_VIRT_EXT
          details.
 
 config SWP_EMULATE
-       bool "Emulate SWP/SWPB instructions"
+       bool "Emulate SWP/SWPB instructions" if !SMP
        depends on CPU_V7
        default y if SMP
        select HAVE_PROC_CPU if PROC_FS