s390/mm: fix vmemmap size calculation

The size of the vmemmap must be a multiple of PAGES_PER_SECTION, since the
common code always initializes the vmemmap in such pieces.
So we must round up in order to not have a too small vmemmap.

Fixes an IPL crash on 31 bit with more than 1920MB.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/setup.c

@@ -571,6 +571,8 @@ static void __init setup_memory_end(void)
 
 	/* Split remaining virtual space between 1:1 mapping & vmemmap array */
 	tmp = VMALLOC_START / (PAGE_SIZE + sizeof(struct page));
+	/* vmemmap contains a multiple of PAGES_PER_SECTION struct pages */
+	tmp = SECTION_ALIGN_UP(tmp);
 	tmp = VMALLOC_START - tmp * sizeof(struct page);
 	tmp &= ~((vmax >> 11) - 1);	/* align to page table level */
 	tmp = min(tmp, 1UL << MAX_PHYSMEM_BITS);