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>

arch/s390/kernel/ipl.c

@@ -1528,15 +1528,12 @@ static struct shutdown_action __refdata dump_action = {
 
 static void dump_reipl_run(struct shutdown_trigger *trigger)
 {
-	struct {
-		void	*addr;
-		__u32	csum;
-	} __packed ipib;
+	unsigned long ipib = (unsigned long) &reipl_block_actual;
+	unsigned int csum;
 
-	ipib.csum = csum_partial(reipl_block_actual,
-				 reipl_block_actual->hdr.len, 0);
-	ipib.addr = reipl_block_actual;
-	memcpy_absolute(&S390_lowcore.ipib, &ipib, sizeof(ipib));
+	csum = csum_partial(reipl_block_actual, reipl_block_actual->hdr.len, 0);
+	mem_assign_absolute(S390_lowcore.ipib, ipib);
+	mem_assign_absolute(S390_lowcore.ipib_checksum, csum);
 	dump_run(trigger);
 }