s390/kasan: use noexec and large pages

To lower memory footprint and speed up kasan initialisation detect
EDAT availability and use large pages if possible. As we know how
much memory is needed for initialisation, another simplistic large
page allocator is introduced to avoid memory fragmentation.

Since facilities list is retrieved anyhow, detect noexec support and
adjust pages attributes. Handle noexec kernel option to avoid inconsistent
kasan shadow memory pages flags.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -468,6 +468,12 @@ static inline int is_module_addr(void *addr)
 				 _SEGMENT_ENTRY_YOUNG |	\
 				 _SEGMENT_ENTRY_PROTECT | \
 				 _SEGMENT_ENTRY_NOEXEC)
+#define SEGMENT_KERNEL_EXEC __pgprot(_SEGMENT_ENTRY |	\
+				 _SEGMENT_ENTRY_LARGE |	\
+				 _SEGMENT_ENTRY_READ |	\
+				 _SEGMENT_ENTRY_WRITE | \
+				 _SEGMENT_ENTRY_YOUNG |	\
+				 _SEGMENT_ENTRY_DIRTY)
 
 /*
  * Region3 entry (large page) protection definitions.

arch/s390/include/asm/setup.h

@@ -65,6 +65,7 @@
 #define OLDMEM_SIZE	(*(unsigned long *)  (OLDMEM_SIZE_OFFSET))
 #define COMMAND_LINE	((char *)	     (COMMAND_LINE_OFFSET))
 
+extern int noexec_disabled;
 extern int memory_end_set;
 extern unsigned long memory_end;
 extern unsigned long max_physmem_end;