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Subject[PATCH mm-unstable RFC 08/26] loongarch/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
Date
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 mk_swap_pte().

Note that this bit does not conflict with swap PMDs and could also be used
in swap PMD context later.

Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/loongarch/include/asm/pgtable-bits.h | 4 +++
arch/loongarch/include/asm/pgtable.h | 39 ++++++++++++++++++++---
2 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/arch/loongarch/include/asm/pgtable-bits.h b/arch/loongarch/include/asm/pgtable-bits.h
index 3d1e0a69975a..8b98d22a145b 100644
--- a/arch/loongarch/include/asm/pgtable-bits.h
+++ b/arch/loongarch/include/asm/pgtable-bits.h
@@ -20,6 +20,7 @@
#define _PAGE_SPECIAL_SHIFT 11
#define _PAGE_HGLOBAL_SHIFT 12 /* HGlobal is a PMD bit */
#define _PAGE_PFN_SHIFT 12
+#define _PAGE_SWP_EXCLUSIVE_SHIFT 23
#define _PAGE_PFN_END_SHIFT 48
#define _PAGE_NO_READ_SHIFT 61
#define _PAGE_NO_EXEC_SHIFT 62
@@ -33,6 +34,9 @@
#define _PAGE_PROTNONE (_ULCAST_(1) << _PAGE_PROTNONE_SHIFT)
#define _PAGE_SPECIAL (_ULCAST_(1) << _PAGE_SPECIAL_SHIFT)

+/* We borrow bit 23 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE (_ULCAST_(1) << _PAGE_SWP_EXCLUSIVE_SHIFT)
+
/* Used by TLB hardware (placed in EntryLo*) */
#define _PAGE_VALID (_ULCAST_(1) << _PAGE_VALID_SHIFT)
#define _PAGE_DIRTY (_ULCAST_(1) << _PAGE_DIRTY_SHIFT)
diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 022ec6be3602..70d037c957a4 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -249,13 +249,26 @@ extern void pud_init(void *addr);
extern void pmd_init(void *addr);

/*
- * Non-present pages: high 40 bits are offset, next 8 bits type,
- * low 16 bits zero.
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ * 6 6 6 6 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3
+ * 3 2 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
+ * <--------------------------- offset ---------------------------
+ *
+ * 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
+ * --------------> E <--- type ---> <---------- zeroes ---------->
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * The zero'ed bits include _PAGE_PRESENT and _PAGE_PROTNONE.
*/
static inline pte_t mk_swap_pte(unsigned long type, unsigned long offset)
-{ pte_t pte; pte_val(pte) = (type << 16) | (offset << 24); return pte; }
+{ pte_t pte; pte_val(pte) = ((type & 0x7f) << 16) | (offset << 24); return pte; }

-#define __swp_type(x) (((x).val >> 16) & 0xff)
+#define __swp_type(x) (((x).val >> 16) & 0x7f)
#define __swp_offset(x) ((x).val >> 24)
#define __swp_entry(type, offset) ((swp_entry_t) { pte_val(mk_swap_pte((type), (offset))) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
@@ -263,6 +276,24 @@ static inline pte_t mk_swap_pte(unsigned long type, unsigned long offset)
#define __pmd_to_swp_entry(pmd) ((swp_entry_t) { pmd_val(pmd) })
#define __swp_entry_to_pmd(x) ((pmd_t) { (x).val | _PAGE_HUGE })

+#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 paging_init(void);

#define pte_none(pte) (!(pte_val(pte) & ~_PAGE_GLOBAL))
--
2.38.1
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