[PATCH 2/2] ARM: domains: add memory dependencies to get_domain/set_domain

Russell King
2015-09-11T09:56:17Z

We need to have memory dependencies on get_domain/set_domain to avoid
the compiler over-optimising these inline assembly instructions.

Loads/stores must not be reordered across a set_domain(), so introduce
a compiler barrier for that assembly.

The value of get_domain() must not be cached across a set_domain(), but
we still want to allow the compiler to optimise it away. Introduce a
dependency on current_thread_info()->cpu_domain to avoid this; the new
memory clobber in set_domain() should therefore cause the compiler to
re-load this. The other advantage of using this is we should have its
address in the register set already, or very soon after at most call
sites.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
arch/arm/include/asm/domain.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/domain.h b/arch/arm/include/asm/domain.h
index e878129f2fee..fc8ba1663601 100644
--- a/arch/arm/include/asm/domain.h
+++ b/arch/arm/include/asm/domain.h
@@ -12,6 +12,7 @@

#ifndef __ASSEMBLY__
#include <asm/barrier.h>
+#include <asm/thread_info.h>
#endif

/*
@@ -89,7 +90,8 @@ static inline unsigned int get_domain(void)

asm(
"mrc p15, 0, %0, c3, c0 @ get domain"
- : "=r" (domain));
+ : "=r" (domain)
+ : "m" (current_thread_info()->cpu_domain));

return domain;
}
@@ -98,7 +100,7 @@ static inline void set_domain(unsigned val)
{
asm volatile(
"mcr p15, 0, %0, c3, c0 @ set domain"
- : : "r" (val));
+ : : "r" (val) : "memory");
isb();
}

--
2.1.0