[PATCH mm-unstable RFC 02/26] alpha/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

David Hildenbrand
2022-12-06T14:48:26Z

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, mask the type in mk_swap_pte() as well.

Note that 32bit alpha has 64bit PTEs but only 32bit swap entries. So the
lower 32bit are zero in a swap PTE and we could have taken a bit in
there as well.

Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/alpha/include/asm/pgtable.h | 41 ++++++++++++++++++++++++++++----
1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/arch/alpha/include/asm/pgtable.h b/arch/alpha/include/asm/pgtable.h
index 9e45f6735d5d..970abf511b13 100644
--- a/arch/alpha/include/asm/pgtable.h
+++ b/arch/alpha/include/asm/pgtable.h
@@ -74,6 +74,9 @@ struct vm_area_struct;
#define _PAGE_DIRTY 0x20000
#define _PAGE_ACCESSED 0x40000

+/* We borrow bit 39 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE 0x8000000000UL
+
/*
* NOTE! The "accessed" bit isn't necessarily exact: it can be kept exactly
* by software (use the KRE/URE/KWE/UWE bits appropriately), but I'll fake it.
@@ -301,18 +304,48 @@ extern inline void update_mmu_cache(struct vm_area_struct * vma,
}

/*
- * Non-present pages: high 24 bits are offset, next 8 bits type,
- * low 32 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 ------------------> E <--- type -->
+ *
+ * 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
+ * <--------------------------- zeroes -------------------------->
+ *
+ * E is the exclusive marker that is not stored in swap entries.
*/
extern inline pte_t mk_swap_pte(unsigned long type, unsigned long offset)
-{ pte_t pte; pte_val(pte) = (type << 32) | (offset << 40); return pte; }
+{ pte_t pte; pte_val(pte) = ((type & 0x7f) << 32) | (offset << 40); return pte; }

-#define __swp_type(x) (((x).val >> 32) & 0xff)
+#define __swp_type(x) (((x).val >> 32) & 0x7f)
#define __swp_offset(x) ((x).val >> 40)
#define __swp_entry(type, off) ((swp_entry_t) { pte_val(mk_swap_pte((type), (off))) })
#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;
+}
+
#define pte_ERROR(e) \
printk("%s:%d: bad pte %016lx.\n", __FILE__, __LINE__, pte_val(e))
#define pmd_ERROR(e) \