m68k/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by stealing one bit from the
type.  Generic MM currently only uses 5 bits for the type
(MAX_SWAPFILES_SHIFT), so the stolen bit is effectively unused.

While at it, make sure for sun3 that the valid bit never gets set by
properly masking it off and mask the type in __swp_entry().

Link: https://lkml.kernel.org/r/20230113171026.582290-11-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/m68k/include/asm/mcf_pgtable.h

@@ -46,6 +46,9 @@
 #define _CACHEMASK040		(~0x060)
 #define _PAGE_GLOBAL040		0x400   /* 68040 global bit, used for kva descs */
 
+/* We borrow bit 7 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	0x080
+
 /*
  * Externally used page protection values.
  */
@@ -254,15 +257,42 @@ static inline pte_t pte_mkcache(pte_t pte)
 extern pgd_t kernel_pg_dir[PTRS_PER_PGD];
 
 /*
- * Encode and de-code a swap entry (must be !pte_none(e) && !pte_present(e))
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ *   <------------------ offset -------------> 0 0 0 E <-- type --->
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
  */
-#define __swp_type(x)		((x).val & 0xFF)
+#define __swp_type(x)		((x).val & 0x7f)
 #define __swp_offset(x)		((x).val >> 11)
-#define __swp_entry(typ, off)	((swp_entry_t) { (typ) | \
+#define __swp_entry(typ, off)	((swp_entry_t) { ((typ) & 0x7f) | \
 					(off << 11) })
 #define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) })
 #define __swp_entry_to_pte(x)	(__pte((x).val))
 
+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+static inline int pte_swp_exclusive(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SWP_EXCLUSIVE;
+}
+
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+	pte_val(pte) |= _PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+	pte_val(pte) &= ~_PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
 #define pmd_pfn(pmd)		(pmd_val(pmd) >> PAGE_SHIFT)
 #define pmd_page(pmd)		(pfn_to_page(pmd_val(pmd) >> PAGE_SHIFT))
 

arch/m68k/include/asm/motorola_pgtable.h

@@ -41,6 +41,9 @@
 
 #define _PAGE_PROTNONE	0x004
 
+/* We borrow bit 11 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	0x800
+
 #ifndef __ASSEMBLY__
 
 /* This is the cache mode to be used for pages containing page descriptors for
@@ -169,12 +172,41 @@ static inline pte_t pte_mkcache(pte_t pte)
 #define swapper_pg_dir kernel_pg_dir
 extern pgd_t kernel_pg_dir[128];
 
-/* Encode and de-code a swap entry (must be !pte_none(e) && !pte_present(e)) */
-#define __swp_type(x)		(((x).val >> 4) & 0xff)
+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ *   <----------------- offset ------------> E <-- type ---> 0 0 0 0
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
+ */
+#define __swp_type(x)		(((x).val >> 4) & 0x7f)
 #define __swp_offset(x)		((x).val >> 12)
-#define __swp_entry(type, offset) ((swp_entry_t) { ((type) << 4) | ((offset) << 12) })
+#define __swp_entry(type, offset) ((swp_entry_t) { (((type) & 0x7f) << 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 })
 
+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+static inline int pte_swp_exclusive(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SWP_EXCLUSIVE;
+}
+
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+	pte_val(pte) |= _PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+	pte_val(pte) &= ~_PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
 #endif	/* !__ASSEMBLY__ */
 #endif /* _MOTOROLA_PGTABLE_H */

arch/m68k/include/asm/sun3_pgtable.h

@@ -71,6 +71,9 @@
 #define SUN3_PMD_MASK	(0x0000003F)
 #define SUN3_PMD_MAGIC	(0x0000002B)
 
+/* We borrow bit 6 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	0x040
+
 #ifndef __ASSEMBLY__
 
 /*
@@ -152,12 +155,42 @@ static inline pte_t pte_mkcache(pte_t pte)	{ return pte; }
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 extern pgd_t kernel_pg_dir[PTRS_PER_PGD];
 
-/* Macros to (de)construct the fake PTEs representing swap pages. */
-#define __swp_type(x)		((x).val & 0x7F)
+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ *   0 <--------------------- offset ----------------> E <- type -->
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
+ */
+#define __swp_type(x)		((x).val & 0x3f)
 #define __swp_offset(x)		(((x).val) >> 7)
-#define __swp_entry(type,offset) ((swp_entry_t) { ((type) | ((offset) << 7)) })
+#define __swp_entry(type, offset) ((swp_entry_t) { (((type) & 0x3f) | \
+						   (((offset) << 7) & ~SUN3_PAGE_VALID)) })
 #define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) })
 #define __swp_entry_to_pte(x)	((pte_t) { (x).val })
 
+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+static inline int pte_swp_exclusive(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SWP_EXCLUSIVE;
+}
+
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+	pte_val(pte) |= _PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+	pte_val(pte) &= ~_PAGE_SWP_EXCLUSIVE;
+	return pte;
+}
+
 #endif	/* !__ASSEMBLY__ */
 #endif	/* !_SUN3_PGTABLE_H */