csky: Fixup swapon

Current csky's swappon is broken by wrong swap PTE entry format.
Now redesign the new format for abiv1 & abiv2 and make swappon +
zram work properly on csky machines.

C-SKY PTE has VALID, DIRTY to emulate PRESENT, READ, WRITE, EXEC
attributes. GLOBAL bit is shared by two pages in the same tlb
entry. So we need to keep GLOBAL, VALID, PRESENT zero in swp_pte.

To distinguish PAGE_NONE and swp_pte, we need to use an additional
bit (abiv1 is _PAGE_READ, abiv2 is _PAGE_WRITE).

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>

Author: guoren83

arch/csky/abiv1/inc/abi/pgtable-bits.h

@@ -24,6 +24,28 @@
 #define _CACHE_CACHED		_PAGE_CACHE
 #define _CACHE_UNCACHED		_PAGE_UNCACHE
 
+#define _PAGE_PROT_NONE		_PAGE_READ
+
+/*
+ * Encode and decode a swap entry
+ *
+ * Format of swap PTE:
+ *     bit          0:    _PAGE_PRESENT (zero)
+ *     bit          1:    _PAGE_READ (zero)
+ *     bit      2 - 5:    swap type[0 - 3]
+ *     bit          6:    _PAGE_GLOBAL (zero)
+ *     bit          7:    _PAGE_VALID (zero)
+ *     bit          8:    swap type[4]
+ *     bit     9 - 31:    swap offset
+ */
+#define __swp_type(x)			((((x).val >> 2) & 0xf) | \
+					(((x).val >> 4) & 0x10))
+#define __swp_offset(x)			((x).val >> 9)
+#define __swp_entry(type, offset)	((swp_entry_t) { \
+					((type & 0xf) << 2) | \
+					((type & 0x10) << 4) | \
+					((offset) << 9)})
+
 #define HAVE_ARCH_UNMAPPED_AREA
 
 #endif /* __ASM_CSKY_PGTABLE_BITS_H */

arch/csky/abiv2/inc/abi/pgtable-bits.h

@@ -24,4 +24,26 @@
 #define _CACHE_CACHED		(_PAGE_CACHE | _PAGE_BUF)
 #define _CACHE_UNCACHED		(0)
 
+#define _PAGE_PROT_NONE		_PAGE_WRITE
+
+/*
+ * Encode and decode a swap entry
+ *
+ * Format of swap PTE:
+ *     bit          0:    _PAGE_GLOBAL (zero)
+ *     bit          1:    _PAGE_VALID (zero)
+ *     bit      2 - 6:    swap type
+ *     bit      7 - 8:    swap offset[0 - 1]
+ *     bit          9:    _PAGE_WRITE (zero)
+ *     bit         10:    _PAGE_PRESENT (zero)
+ *     bit    11 - 31:    swap offset[2 - 22]
+ */
+#define __swp_type(x)			(((x).val >> 2) & 0x1f)
+#define __swp_offset(x)			((((x).val >> 7) & 0x3) | \
+					(((x).val >> 9) & 0x7ffffc))
+#define __swp_entry(type, offset)	((swp_entry_t) { \
+					((type & 0x1f) << 2) | \
+					((offset & 0x3) << 7) | \
+					((offset & 0x7ffffc) << 9)})
+
 #endif /* __ASM_CSKY_PGTABLE_BITS_H */

arch/csky/include/asm/pgtable.h

@@ -41,13 +41,6 @@
 #define pfn_pte(pfn, prot) __pte(((unsigned long long)(pfn) << PAGE_SHIFT) \
 				| pgprot_val(prot))
 
-#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_MODIFIED | \
-			 _CACHE_MASK)
-
-#define __swp_type(x)			(((x).val >> 4) & 0xff)
-#define __swp_offset(x)			((x).val >> 12)
-#define __swp_entry(type, offset)	((swp_entry_t) {((type) << 4) | \
-					((offset) << 12) })
 #define __pte_to_swp_entry(pte)		((swp_entry_t) { pte_val(pte) })
 #define __swp_entry_to_pte(x)		((pte_t) { (x).val })
 
@@ -61,8 +54,7 @@
  */
 #define _PAGE_BASE	(_PAGE_PRESENT | _PAGE_ACCESSED)
 
-#define PAGE_NONE	__pgprot(_PAGE_BASE | \
-				_CACHE_CACHED)
+#define PAGE_NONE	__pgprot(_PAGE_PROT_NONE)
 #define PAGE_READ	__pgprot(_PAGE_BASE | _PAGE_READ | \
 				_CACHE_CACHED)
 #define PAGE_WRITE	__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_WRITE | \
@@ -79,6 +71,13 @@
 				_PAGE_GLOBAL | \
 				_CACHE_UNCACHED | _PAGE_SO)
 
+#define _PAGE_CHG_MASK	(~(unsigned long) \
+				(_PAGE_PRESENT | _PAGE_READ | _PAGE_WRITE | \
+				_CACHE_MASK | _PAGE_GLOBAL))
+
+#define MAX_SWAPFILES_CHECK() \
+		BUILD_BUG_ON(MAX_SWAPFILES_SHIFT != 5)
+
 #define __P000	PAGE_NONE
 #define __P001	PAGE_READ
 #define __P010	PAGE_READ