Commit 6e8f580d authored Sep 11, 2015 by Russell King

ARM: domains: add memory dependencies to get_domain/set_domain



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.

Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

parent 716ff192

arch/arm/include/asm/domain.h

+4 −2

Original line number	Diff line number	Diff line
		@@ -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();
		}