x86/speculation/mds: Eliminate leaks by trace_hardirqs_on()

Move mds_idle_clear_cpu_buffers() after trace_hardirqs_on() to ensure
all store buffer entries are flushed.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: jgross@suse.com
Cc: ndesaulniers@google.com
Cc: gregkh@linuxfoundation.org
Link: https://lkml.kernel.org/r/1561260904-29669-2-git-send-email-zhenzhong.duan@oracle.com

arch/x86/include/asm/mwait.h

@@ -86,9 +86,9 @@ static inline void __mwaitx(unsigned long eax, unsigned long ebx,
 
 static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
 {
-	mds_idle_clear_cpu_buffers();
-
 	trace_hardirqs_on();
+
+	mds_idle_clear_cpu_buffers();
 	/* "mwait %eax, %ecx;" */
 	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
 		     :: "a" (eax), "c" (ecx));