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>

3 files changed, 11 insertions, 8 deletions

diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 47853debb3b..a47c6e221a9 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -302,12 +302,7 @@ struct _lowcore {
 	 */
 	__u64	ipib;				/* 0x0e00 */
 	__u32	ipib_checksum;			/* 0x0e08 */
-	/*
-	 * Because the vmcore_info pointer is not 8 byte aligned it never
-	 * should not be accessed directly. For accessing the pointer, first
-	 * copy it to a local pointer variable.
-	 */
-	__u8	vmcore_info[8];			/* 0x0e0c */
+	__u64	vmcore_info;			/* 0x0e0c */
 	__u8	pad_0x0e14[0x0e18-0x0e14];	/* 0x0e14 */
 	__u64	os_info;			/* 0x0e18 */
 	__u8	pad_0x0e20[0x0f00-0x0e20];	/* 0x0e20 */
diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 20d0585cf90..f1700c5c888 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -348,4 +348,14 @@ extern void (*s390_base_ext_handler_fn)(void);
 	".previous\n"
 #endif
 
+extern int memcpy_real(void *, void *, size_t);
+extern void memcpy_absolute(void *, void *, size_t);
+
+#define mem_assign_absolute(dest, val) {			\
+	__typeof__(dest) __tmp = (val);				\
+								\
+	BUILD_BUG_ON(sizeof(__tmp) != sizeof(val));		\
+	memcpy_absolute(&(dest), &__tmp, sizeof(__tmp));	\
+}
+
 #endif                                 /* __ASM_S390_PROCESSOR_H           */
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index 1f3a79bcd26..7e7285179aa 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -381,8 +381,6 @@ clear_user(void __user *to, unsigned long n)
 	return n;
 }
 
-extern int memcpy_real(void *, void *, size_t);
-extern void memcpy_absolute(void *, void *, size_t);
 extern int copy_to_user_real(void __user *dest, void *src, size_t count);
 extern int copy_from_user_real(void *dest, void __user *src, size_t count);