ia64/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, also mask the type in __swp_entry().

Link: https://lkml.kernel.org/r/20230113171026.582290-8-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/ia64/include/asm/pgtable.h

@@ -58,6 +58,9 @@
 #define _PAGE_ED		(__IA64_UL(1) << 52)	/* exception deferral */
 #define _PAGE_PROTNONE		(__IA64_UL(1) << 63)
 
+/* We borrow bit 7 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	(1 << 7)
+
 #define _PFN_MASK		_PAGE_PPN_MASK
 /* Mask of bits which may be changed by pte_modify(); the odd bits are there for _PAGE_PROTNONE */
 #define _PAGE_CHG_MASK	(_PAGE_P | _PAGE_PROTNONE | _PAGE_PL_MASK | _PAGE_AR_MASK | _PAGE_ED)
@@ -399,6 +402,9 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 extern void paging_init (void);
 
 /*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
  * Note: The macros below rely on the fact that MAX_SWAPFILES_SHIFT <= number of
  *	 bits in the swap-type field of the swap pte.  It would be nice to
  *	 enforce that, but we can't easily include <linux/swap.h> here.
@@ -406,16 +412,36 @@ extern void paging_init (void);
  *
  * Format of swap pte:
  *	bit   0   : present bit (must be zero)
- *	bits  1- 7: swap-type
+ *	bits  1- 6: swap type
+ *	bit   7   : exclusive marker
  *	bits  8-62: swap offset
  *	bit  63   : _PAGE_PROTNONE bit
  */
-#define __swp_type(entry)		(((entry).val >> 1) & 0x7f)
+#define __swp_type(entry)		(((entry).val >> 1) & 0x3f)
 #define __swp_offset(entry)		(((entry).val << 1) >> 9)
-#define __swp_entry(type,offset)	((swp_entry_t) { ((type) << 1) | ((long) (offset) << 8) })
+#define __swp_entry(type, offset)	((swp_entry_t) { ((type & 0x3f) << 1) | \
+							 ((long) (offset) << 8) })
 #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;
+}
+
 /*
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..