[tip:x86/idle] x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers

["tip-bot for H. Peter Anvin" <tipbot@xxxxxxxxx>]

Commit-ID:  7e98b71920464b8d15fa95c74366416cd3c88861
Gitweb:     http://git.kernel.org/tip/7e98b71920464b8d15fa95c74366416cd3c88861
Author:     H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
AuthorDate: Thu, 19 Dec 2013 11:58:16 -0800
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Thu, 19 Dec 2013 11:58:16 -0800

x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers

Use static_cpu_has() to conditionalize the CLFLUSH workaround, and add
memory barriers around it since the documentation is explicit that
CLFLUSH is only ordered with respect to MFENCE.

Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Link: http://lkml.kernel.org/r/CA%2B55aFzGxcML7j8CEvQPYzh0W81uVoAAVmGctMOUZ7CZ1yYd2A@xxxxxxxxxxxxxx
---
 arch/x86/include/asm/mwait.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 361b02e..19b71c4 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -43,8 +43,11 @@ static inline void __mwait(unsigned long eax, unsigned long ecx)
 static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
 {
 	if (!current_set_polling_and_test()) {
-		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+		if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
+			mb();
 			clflush((void *)&current_thread_info()->flags);
+			mb();
+		}
 
 		__monitor((void *)&current_thread_info()->flags, 0, 0);
 		if (!need_resched())
--
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