nios2/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using the yet-unused bit
31.

Link: https://lkml.kernel.org/r/20230113171026.582290-15-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/nios2/include/asm/pgtable-bits.h

@@ -31,4 +31,7 @@
 #define _PAGE_ACCESSED	(1<<26)	/* page referenced */
 #define _PAGE_DIRTY	(1<<27)	/* dirty page */
 
+/* We borrow bit 31 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	(1<<31)
+
 #endif /* _ASM_NIOS2_PGTABLE_BITS_H */

arch/nios2/include/asm/pgtable.h

@@ -239,7 +239,9 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
  *
  *   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 < type -> 0 0 0 0 0 0 <-------------- offset --------------->
+ *   E < type -> 0 0 0 0 0 0 <-------------- offset --------------->
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
  *
  * Note that the offset field is always non-zero if the swap type is 0, thus
  * !pte_none() is always true.
@@ -251,6 +253,24 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
 #define __swp_entry_to_pte(swp)	((pte_t) { (swp).val })
 #define __pte_to_swp_entry(pte)	((swp_entry_t) { pte_val(pte) })
 
+#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;
+}
+
 extern void __init paging_init(void);
 extern void __init mmu_init(void);