[S390] add support for physical memory > 4TB

The kernel address space of a 64 bit kernel currently uses a three level
page table and the vmemmap array has a fixed address and a fixed maximum
size. A three level page table is good enough for systems with less than
3.8TB of memory, for bigger systems four page table levels need to be
used. Each page table level costs a bit of performance, use 3 levels for
normal systems and 4 levels only for the really big systems.
To avoid bloating sparse.o too much set MAX_PHYSMEM_BITS to 46 for a
maximum of 64TB of memory.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -128,28 +128,11 @@ static inline int is_zero_pfn(unsigned long pfn)
  * effect, this also makes sure that 64 bit module code cannot be used
  * as system call address.
  */
-
 extern unsigned long VMALLOC_START;
+extern unsigned long VMALLOC_END;
+extern struct page *vmemmap;
 
-#ifndef __s390x__
-#define VMALLOC_SIZE	(96UL << 20)
-#define VMALLOC_END	0x7e000000UL
-#define VMEM_MAP_END	0x80000000UL
-#else /* __s390x__ */
-#define VMALLOC_SIZE	(128UL << 30)
-#define VMALLOC_END	0x3e000000000UL
-#define VMEM_MAP_END	0x40000000000UL
-#endif /* __s390x__ */
-
-/*
- * VMEM_MAX_PHYS is the highest physical address that can be added to the 1:1
- * mapping. This needs to be calculated at compile time since the size of the
- * VMEM_MAP is static but the size of struct page can change.
- */
-#define VMEM_MAX_PAGES	((VMEM_MAP_END - VMALLOC_END) / sizeof(struct page))
-#define VMEM_MAX_PFN	min(VMALLOC_START >> PAGE_SHIFT, VMEM_MAX_PAGES)
-#define VMEM_MAX_PHYS	((VMEM_MAX_PFN << PAGE_SHIFT) & ~((16 << 20) - 1))
-#define vmemmap		((struct page *) VMALLOC_END)
+#define VMEM_MAX_PHYS ((unsigned long) vmemmap)
 
 /*
  * A 31 bit pagetable entry of S390 has following format:

arch/s390/include/asm/sparsemem.h

@@ -4,8 +4,8 @@
 #ifdef CONFIG_64BIT
 
 #define SECTION_SIZE_BITS	28
-#define MAX_PHYSADDR_BITS	42
-#define MAX_PHYSMEM_BITS	42
+#define MAX_PHYSADDR_BITS	46
+#define MAX_PHYSMEM_BITS	46
 
 #else
 

arch/s390/kernel/setup.c

@@ -94,6 +94,15 @@ struct mem_chunk __initdata memory_chunk[MEMORY_CHUNKS];
 int __initdata memory_end_set;
 unsigned long __initdata memory_end;
 
+unsigned long VMALLOC_START;
+EXPORT_SYMBOL(VMALLOC_START);
+
+unsigned long VMALLOC_END;
+EXPORT_SYMBOL(VMALLOC_END);
+
+struct page *vmemmap;
+EXPORT_SYMBOL(vmemmap);
+
 /* An array with a pointer to the lowcore of every CPU. */
 struct _lowcore *lowcore_ptr[NR_CPUS];
 EXPORT_SYMBOL(lowcore_ptr);
@@ -277,6 +286,15 @@ static int __init early_parse_mem(char *p)
 }
 early_param("mem", early_parse_mem);
 
+static int __init parse_vmalloc(char *arg)
+{
+	if (!arg)
+		return -EINVAL;
+	VMALLOC_END = (memparse(arg, &arg) + PAGE_SIZE - 1) & PAGE_MASK;
+	return 0;
+}
+early_param("vmalloc", parse_vmalloc);
+
 unsigned int user_mode = HOME_SPACE_MODE;
 EXPORT_SYMBOL_GPL(user_mode);
 
@@ -478,8 +496,7 @@ EXPORT_SYMBOL_GPL(real_memory_size);
 
 static void __init setup_memory_end(void)
 {
-	unsigned long memory_size;
-	unsigned long max_mem;
+	unsigned long vmax, vmalloc_size, tmp;
 	int i;
 
 
@@ -489,12 +506,9 @@ static void __init setup_memory_end(void)
 		memory_end_set = 1;
 	}
 #endif
-	memory_size = 0;
+	real_memory_size = 0;
 	memory_end &= PAGE_MASK;
 
-	max_mem = memory_end ? min(VMEM_MAX_PHYS, memory_end) : VMEM_MAX_PHYS;
-	memory_end = min(max_mem, memory_end);
-
 	/*
 	 * Make sure all chunks are MAX_ORDER aligned so we don't need the
 	 * extra checks that HOLES_IN_ZONE would require.
@@ -514,23 +528,48 @@ static void __init setup_memory_end(void)
 			chunk->addr = start;
 			chunk->size = end - start;
 		}
+		real_memory_size = max(real_memory_size,
+				       chunk->addr + chunk->size);
 	}
 
+	/* Choose kernel address space layout: 2, 3, or 4 levels. */
+#ifdef CONFIG_64BIT
+	vmalloc_size = VMALLOC_END ?: 128UL << 30;
+	tmp = (memory_end ?: real_memory_size) / PAGE_SIZE;
+	tmp = tmp * (sizeof(struct page) + PAGE_SIZE) + vmalloc_size;
+	if (tmp <= (1UL << 42))
+		vmax = 1UL << 42;	/* 3-level kernel page table */
+	else
+		vmax = 1UL << 53;	/* 4-level kernel page table */
+#else
+	vmalloc_size = VMALLOC_END ?: 96UL << 20;
+	vmax = 1UL << 31;		/* 2-level kernel page table */
+#endif
+	/* vmalloc area is at the end of the kernel address space. */
+	VMALLOC_END = vmax;
+	VMALLOC_START = vmax - vmalloc_size;
+
+	/* Split remaining virtual space between 1:1 mapping & vmemmap array */
+	tmp = VMALLOC_START / (PAGE_SIZE + sizeof(struct page));
+	tmp = VMALLOC_START - tmp * sizeof(struct page);
+	tmp &= ~((vmax >> 11) - 1);	/* align to page table level */
+	tmp = min(tmp, 1UL << MAX_PHYSMEM_BITS);
+	vmemmap = (struct page *) tmp;
+
+	/* Take care that memory_end is set and <= vmemmap */
+	memory_end = min(memory_end ?: real_memory_size, tmp);
+
+	/* Fixup memory chunk array to fit into 0..memory_end */
 	for (i = 0; i < MEMORY_CHUNKS; i++) {
 		struct mem_chunk *chunk = &memory_chunk[i];
 
-		real_memory_size = max(real_memory_size,
-				       chunk->addr + chunk->size);
-		if (chunk->addr >= max_mem) {
+		if (chunk->addr >= memory_end) {
 			memset(chunk, 0, sizeof(*chunk));
 			continue;
 		}
-		if (chunk->addr + chunk->size > max_mem)
-			chunk->size = max_mem - chunk->addr;
-		memory_size = max(memory_size, chunk->addr + chunk->size);
+		if (chunk->addr + chunk->size > memory_end)
+			chunk->size = memory_end - chunk->addr;
 	}
-	if (!memory_end)
-		memory_end = memory_size;
 }
 
 void *restart_stack __attribute__((__section__(".data")));

arch/s390/mm/init.c

@@ -93,18 +93,22 @@ static unsigned long setup_zero_pages(void)
 void __init paging_init(void)
 {
 	unsigned long max_zone_pfns[MAX_NR_ZONES];
-	unsigned long pgd_type;
+	unsigned long pgd_type, asce_bits;
 
 	init_mm.pgd = swapper_pg_dir;
-	S390_lowcore.kernel_asce = __pa(init_mm.pgd) & PAGE_MASK;
 #ifdef CONFIG_64BIT
-	/* A three level page table (4TB) is enough for the kernel space. */
-	S390_lowcore.kernel_asce |= _ASCE_TYPE_REGION3 | _ASCE_TABLE_LENGTH;
+	if (VMALLOC_END > (1UL << 42)) {
+		asce_bits = _ASCE_TYPE_REGION2 | _ASCE_TABLE_LENGTH;
+		pgd_type = _REGION2_ENTRY_EMPTY;
+	} else {
+		asce_bits = _ASCE_TYPE_REGION3 | _ASCE_TABLE_LENGTH;
 		pgd_type = _REGION3_ENTRY_EMPTY;
+	}
 #else
-	S390_lowcore.kernel_asce |= _ASCE_TABLE_LENGTH;
+	asce_bits = _ASCE_TABLE_LENGTH;
 	pgd_type = _SEGMENT_ENTRY_EMPTY;
 #endif
+	S390_lowcore.kernel_asce = (__pa(init_mm.pgd) & PAGE_MASK) | asce_bits;
 	clear_table((unsigned long *) init_mm.pgd, pgd_type,
 		    sizeof(unsigned long)*2048);
 	vmem_map_init();

arch/s390/mm/pgtable.c

@@ -33,17 +33,6 @@
 #define FRAG_MASK	0x03
 #endif
 
-unsigned long VMALLOC_START = VMALLOC_END - VMALLOC_SIZE;
-EXPORT_SYMBOL(VMALLOC_START);
-
-static int __init parse_vmalloc(char *arg)
-{
-	if (!arg)
-		return -EINVAL;
-	VMALLOC_START = (VMALLOC_END - memparse(arg, &arg)) & PAGE_MASK;
-	return 0;
-}
-early_param("vmalloc", parse_vmalloc);
 
 unsigned long *crst_table_alloc(struct mm_struct *mm)
 {