[PATCH mm-unstable RFC 03/26] arc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

David Hildenbrand
2022-12-06T14:51:08Z

Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE by using bit 5, which is yet
unused. The only important parts seems to be to not use _PAGE_PRESENT
(bit 9).

Cc: Vineet Gupta <vgupta@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
arch/arc/include/asm/pgtable-bits-arcv2.h | 27 ++++++++++++++++++++---
1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/arc/include/asm/pgtable-bits-arcv2.h b/arch/arc/include/asm/pgtable-bits-arcv2.h
index 515e82db519f..611f412713b9 100644
--- a/arch/arc/include/asm/pgtable-bits-arcv2.h
+++ b/arch/arc/include/asm/pgtable-bits-arcv2.h
@@ -26,6 +26,9 @@
#define _PAGE_GLOBAL (1 << 8) /* ASID agnostic (H) */
#define _PAGE_PRESENT (1 << 9) /* PTE/TLB Valid (H) */

+/* We borrow bit 5 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE _PAGE_DIRTY
+
#ifdef CONFIG_ARC_MMU_V4
#define _PAGE_HW_SZ (1 << 10) /* Normal/super (H) */
#else
@@ -106,9 +109,18 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
pte_t *ptep);

-/* Encode swap {type,off} tuple into PTE
- * We reserve 13 bits for 5-bit @type, keeping bits 12-5 zero, ensuring that
- * PAGE_PRESENT is zero in a PTE holding swap "identifier"
+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ * 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
+ * <-------------- offset -------------> <--- zero --> E < type ->
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * The zero'ed bits include _PAGE_PRESENT.
*/
#define __swp_entry(type, off) ((swp_entry_t) \
{ ((type) & 0x1f) | ((off) << 13) })
@@ -120,6 +132,15 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
#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;
+}
+
+PTE_BIT_FUNC(swp_mkexclusive, |= (_PAGE_SWP_EXCLUSIVE));
+PTE_BIT_FUNC(swp_clear_exclusive, &= ~(_PAGE_SWP_EXCLUSIVE));
+
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
#include <asm/hugepage.h>
#endif
--
2.38.1