From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Thu, 7 Sep 2017 17:03:19 +0200
Subject: s390: add stack switch helper
Git-commit: ff340d2472ec7618443913928af9fb85a7009270
Patch-mainline: v4.20-rc1
References: jsc#SLE-11178

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
 arch/s390/include/asm/processor.h | 49 +++++++++++++++++++++++++++++++++++++++
 arch/s390/kernel/irq.c            | 10 +-------
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 7f2953c15c37..43494a014d5b 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -250,6 +250,55 @@ static inline unsigned short stap(void)
 	return cpu_address;
 }
 
+#define CALL_ARGS_0()							\
+	register unsigned long r2 asm("2")
+#define CALL_ARGS_1(arg1)						\
+	register unsigned long r2 asm("2") = (unsigned long)(arg1)
+#define CALL_ARGS_2(arg1, arg2)						\
+	CALL_ARGS_1(arg1);						\
+	register unsigned long r3 asm("3") = (unsigned long)(arg2)
+#define CALL_ARGS_3(arg1, arg2, arg3)					\
+	CALL_ARGS_2(arg1, arg2);					\
+	register unsigned long r4 asm("4") = (unsigned long)(arg3)
+#define CALL_ARGS_4(arg1, arg2, arg3, arg4)				\
+	CALL_ARGS_3(arg1, arg2, arg3);					\
+	register unsigned long r4 asm("5") = (unsigned long)(arg4)
+#define CALL_ARGS_5(arg1, arg2, arg3, arg4, arg5)			\
+	CALL_ARGS_4(arg1, arg2, arg3, arg4);				\
+	register unsigned long r4 asm("6") = (unsigned long)(arg5)
+
+#define CALL_FMT_0
+#define CALL_FMT_1 CALL_FMT_0, "0" (r2)
+#define CALL_FMT_2 CALL_FMT_1, "d" (r3)
+#define CALL_FMT_3 CALL_FMT_2, "d" (r4)
+#define CALL_FMT_4 CALL_FMT_3, "d" (r5)
+#define CALL_FMT_5 CALL_FMT_4, "d" (r6)
+
+#define CALL_CLOBBER_5 "0", "1", "14", "cc", "memory"
+#define CALL_CLOBBER_4 CALL_CLOBBER_5
+#define CALL_CLOBBER_3 CALL_CLOBBER_4, "5"
+#define CALL_CLOBBER_2 CALL_CLOBBER_3, "4"
+#define CALL_CLOBBER_1 CALL_CLOBBER_2, "3"
+#define CALL_CLOBBER_0 CALL_CLOBBER_1
+
+#define CALL_ON_STACK(fn, stack, nr, args...)				\
+({									\
+	CALL_ARGS_##nr(args);						\
+	unsigned long prev;						\
+									\
+	asm volatile(							\
+		"	la	%[_prev],0(15)\n"			\
+		"	la	15,0(%[_stack])\n"			\
+		"	stg	%[_prev],%[_bc](15)\n"			\
+		"	brasl	14,%[_fn]\n"				\
+		"	la	15,0(%[_prev])\n"			\
+		: "+&d" (r2), [_prev] "=&a" (prev)			\
+		: [_stack] "a" (stack),					\
+		  [_bc] "i" (offsetof(struct stack_frame, back_chain)),	\
+		  [_fn] "X" (fn) CALL_FMT_##nr : CALL_CLOBBER_##nr);	\
+	r2;								\
+})
+
 /*
  * Give up the time slice of the virtual PU.
  */
diff --git a/arch/s390/kernel/irq.c b/arch/s390/kernel/irq.c
index 3d17c41074ca..0e8d68bac82c 100644
--- a/arch/s390/kernel/irq.c
+++ b/arch/s390/kernel/irq.c
@@ -172,15 +172,7 @@ void do_softirq_own_stack(void)
 	/* Check against async. stack address range. */
 	new = S390_lowcore.async_stack;
 	if (((new - old) >> (PAGE_SHIFT + THREAD_SIZE_ORDER)) != 0) {
-		/* Need to switch to the async. stack. */
-		new -= STACK_FRAME_OVERHEAD;
-		((struct stack_frame *) new)->back_chain = old;
-		asm volatile("   la    15,0(%0)\n"
-			     "   brasl 14,__do_softirq\n"
-			     "   la    15,0(%1)\n"
-			     : : "a" (new), "a" (old)
-			     : "0", "1", "2", "3", "4", "5", "14",
-			       "cc", "memory" );
+		CALL_ON_STACK(__do_softirq, new, 0);
 	} else {
 		/* We are already on the async stack. */
 		__do_softirq();