s390/smp: make absolute lowcore / cpu restart parameter accesses more robust

Setting the cpu restart parameters is done in three different fashions:
- directly setting the four parameters individually
- copying the four parameters with memcpy (using 4 * sizeof(long))
- copying the four parameters using a private structure

In addition code in entry*.S relies on a certain order of the restart
members of struct _lowcore.

Make all of this more robust to future changes by adding a
mem_absolute_assign(dest, val) define, which assigns val to dest
using absolute addressing mode. Also the load multiple instructions
in entry*.S have been split into separate load instruction so the
order of the struct _lowcore members doesn't matter anymore.

In addition move the prototypes of memcpy_real/absolute from uaccess.h
to processor.h. These memcpy* variants are not related to uaccess at all.
string.h doesn't seem to match as well, so lets use processor.h.

Also replace the eight byte array in struct _lowcore which represents a
misaliged u64 with a u64. The compiler will always create code that
handles the misaligned u64 correctly.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 7 insertions, 9 deletions

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index e014084..dc602a6 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -273,26 +273,24 @@ static void pcpu_delegate(struct pcpu *pcpu, void (*func)(void *),
 			  void *data, unsigned long stack)
 {
 	struct _lowcore *lc = lowcore_ptr[pcpu - pcpu_devices];
-	struct {
-		unsigned long	stack;
-		void		*func;
-		void		*data;
-		unsigned long	source;
-	} restart = { stack, func, data, stap() };
+	unsigned long source_cpu = stap();
 
 	__load_psw_mask(psw_kernel_bits);
-	if (pcpu->address == restart.source)
+	if (pcpu->address == source_cpu)
 		func(data);	/* should not return */
 	/* Stop target cpu (if func returns this stops the current cpu). */
 	pcpu_sigp_retry(pcpu, SIGP_STOP, 0);
 	/* Restart func on the target cpu and stop the current cpu. */
-	memcpy_absolute(&lc->restart_stack, &restart, sizeof(restart));
+	mem_assign_absolute(lc->restart_stack, stack);
+	mem_assign_absolute(lc->restart_fn, (unsigned long) func);
+	mem_assign_absolute(lc->restart_data, (unsigned long) data);
+	mem_assign_absolute(lc->restart_source, source_cpu);
 	asm volatile(
 		"0:	sigp	0,%0,%2	# sigp restart to target cpu\n"
 		"	brc	2,0b	# busy, try again\n"
 		"1:	sigp	0,%1,%3	# sigp stop to current cpu\n"
 		"	brc	2,1b	# busy, try again\n"
-		: : "d" (pcpu->address), "d" (restart.source),
+		: : "d" (pcpu->address), "d" (source_cpu),
 		    "K" (SIGP_RESTART), "K" (SIGP_STOP)
 		: "0", "1", "cc");
 	for (;;) ;