[PATCH mm-unstable v1 25/26] xtensa/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

David Hildenbrand
2023-01-13T17:21:18Z

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using bit 1. This
bit should be safe to use for our usecase.

Most importantly, we can still distinguish swap PTEs from PAGE_NONE PTEs
(see pte_present()) and don't use one of the two reserved attribute
masks (1101 and 1111). Attribute mask 1100 and 1110 now identify swap PTEs.

While at it, remove SWP_TYPE_BITS (not really helpful as it's not used in
the actual swap macros) and mask the type in __swp_entry().

Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/xtensa/include/asm/pgtable.h | 32 ++++++++++++++++++++++++++-----
1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/arch/xtensa/include/asm/pgtable.h b/arch/xtensa/include/asm/pgtable.h
index 5b5484d707b2..1025e2dc292b 100644
--- a/arch/xtensa/include/asm/pgtable.h
+++ b/arch/xtensa/include/asm/pgtable.h
@@ -96,7 +96,7 @@
* +- - - - - - - - - - - - - - - - - - - - -+
* (PAGE_NONE)| PPN | 0 | 00 | ADW | 01 | 11 | 11 |
* +-----------------------------------------+
- * swap | index | type | 01 | 11 | 00 |
+ * swap | index | type | 01 | 11 | e0 |
* +-----------------------------------------+
*
* For T1050 hardware and earlier the layout differs for present and (PAGE_NONE)
@@ -112,6 +112,7 @@
* RI ring (0=privileged, 1=user, 2 and 3 are unused)
* CA cache attribute: 00 bypass, 01 writeback, 10 writethrough
* (11 is invalid and used to mark pages that are not present)
+ * e exclusive marker in swap PTEs
* w page is writable (hw)
* x page is executable (hw)
* index swap offset / PAGE_SIZE (bit 11-31: 21 bits -> 8 GB)
@@ -158,6 +159,9 @@
#define _PAGE_DIRTY (1<<7) /* software: page dirty */
#define _PAGE_ACCESSED (1<<8) /* software: page accessed (read) */

+/* We borrow bit 1 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE (1<<1)
+
#ifdef CONFIG_MMU

#define _PAGE_CHG_MASK (PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
@@ -343,19 +347,37 @@ ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
}

/*
- * Encode and decode a swap and file entry.
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
*/
-#define SWP_TYPE_BITS 5
-#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS)
+#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > 5)

#define __swp_type(entry) (((entry).val >> 6) & 0x1f)
#define __swp_offset(entry) ((entry).val >> 11)
#define __swp_entry(type,offs) \
- ((swp_entry_t){((type) << 6) | ((offs) << 11) | \
+ ((swp_entry_t){(((type) & 0x1f) << 6) | ((offs) << 11) | \
_PAGE_CA_INVALID | _PAGE_USER})
#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 /* !defined (__ASSEMBLY__) */

--
2.39.0