[RESEND v7 06/29] s390: mm: add PMD swap-exclusive helpers

[Usama Arif <usama.arif@linux.dev>]

A later patch keeps a PMD-mapped anonymous THP mapped by a PMD across the
swap round-trip, so PG_anon_exclusive now has to survive in a swap PMD and
not just in a swap PTE.

s390 is the one architecture where a swap PMD is not a swap PTE in
disguise: it is an RSTE with its own layout, converted to a fake PTE swap
entry for the common code. Give it its own exclusive bit rather than
borrowing the PTE-format macro. The two happen to have the same value, but
that is a coincidence. Bit 52 was documented as unused; document what it
is now.

Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Usama Arif <usama.arif@linux.dev>
---
 arch/s390/include/asm/pgtable.h | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 2d5c2ab06de98..0790a0884cfab 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -333,6 +333,7 @@ void setup_protection_map(void);
 /* Common bits in region and segment table entries, for swap entries */
 #define _RST_ENTRY_COMM		0x0010	/* Common-Region/Segment, marks swap entry */
 #define _RST_ENTRY_INVALID	0x0020	/* invalid region/segment table entry */
+#define _RST_ENTRY_SWP_EXCLUSIVE 0x0800	/* SW exclusive swap bit, see mk_swap_rste() */
 
 #define _CRST_ENTRIES	2048	/* number of region/segment table entries */
 #define _PAGE_ENTRIES	256	/* number of page table entries	*/
@@ -859,6 +860,28 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
 	return clear_pte_bit(pte, __pgprot(_PAGE_SWP_EXCLUSIVE));
 }
 
+#ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
+/*
+ * A PMD swap entry is an RSTE, not a PTE, so it needs its own exclusive bit
+ * rather than the PTE-format _PAGE_SWP_EXCLUSIVE.  The two happen to have the
+ * same value; see the RSTE swap layout above mk_swap_rste().
+ */
+static inline pmd_t pmd_swp_mkexclusive(pmd_t pmd)
+{
+	return set_pmd_bit(pmd, __pgprot(_RST_ENTRY_SWP_EXCLUSIVE));
+}
+
+static inline bool pmd_swp_exclusive(pmd_t pmd)
+{
+	return pmd_val(pmd) & _RST_ENTRY_SWP_EXCLUSIVE;
+}
+
+static inline pmd_t pmd_swp_clear_exclusive(pmd_t pmd)
+{
+	return clear_pmd_bit(pmd, __pgprot(_RST_ENTRY_SWP_EXCLUSIVE));
+}
+#endif
+
 static inline int pte_soft_dirty(pte_t pte)
 {
 	return pte_val(pte) & _PAGE_SOFT_DIRTY;
@@ -1900,15 +1923,16 @@ static inline swp_entry_t __swp_entry(unsigned long type, unsigned long offset)
  * Bits 59 and 63 are used to indicate the swap entry. Bit 58 marks the rste
  * as invalid.
  * A swap entry is indicated by bit pattern (rste & 0x011) == 0x010
- * |			  offset			|Xtype |11TT|S0|
+ * |			  offset			|Etype |11TT|S0|
  * |0000000000111111111122222222223333333333444444444455|555555|5566|66|
  * |0123456789012345678901234567890123456789012345678901|234567|8901|23|
  *
  * Bits 0-51 store the offset.
+ * Bit 52 (E) is used to remember PG_anon_exclusive
+ * (_RST_ENTRY_SWP_EXCLUSIVE), mirroring bit 52 of a swap pte.
  * Bits 53-57 store the type.
  * Bit 62 (S) is used for softdirty tracking.
  * Bits 60-61 (TT) indicate the table type: 0x01 for REGION3 and 0x00 for SEGMENT.
- * Bit 52 (X) is unused.
  */
 
 #define __SWP_OFFSET_MASK_RSTE	((1UL << 52) - 1)
-- 
2.53.0-Meta