[PATCH mm-unstable RFC 12/26] mips/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

From: David Hildenbrand
Date: Tue Dec 06 2022 - 09:53:55 EST

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Let's support __HAVE_ARCH_PTE_SWP_EXCLUSIVE.

On 64bit, steal 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.

On 32bit we're able to locate unused bits. As the PTE layout for 32 bit
is very confusing, document it a bit better.

While at it, mask the type in __swp_entry()/mk_swap_pte().

Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
arch/mips/include/asm/pgtable-32.h | 86 ++++++++++++++++++++++++++----
arch/mips/include/asm/pgtable-64.h | 23 ++++++--
arch/mips/include/asm/pgtable.h | 36 +++++++++++++
3 files changed, 130 insertions(+), 15 deletions(-)

diff --git a/arch/mips/include/asm/pgtable-32.h b/arch/mips/include/asm/pgtable-32.h
index b40a0e69fccc..c2a3b899480c 100644
--- a/arch/mips/include/asm/pgtable-32.h
+++ b/arch/mips/include/asm/pgtable-32.h
@@ -191,42 +191,103 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)

#define pte_page(x) pfn_to_page(pte_pfn(x))

+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ */
#if defined(CONFIG_CPU_R3K_TLB)

-/* Swap entries must have VALID bit cleared. */
+/*
+ * 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 ------------> < type -> V G E 0 0 0 0 0 0 P
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * _PAGE_PRESENT (P), _PAGE_VALID (V) and_PAGE_GLOBAL (G) have to remain
+ * unused.
+ */
#define __swp_type(x) (((x).val >> 10) & 0x1f)
#define __swp_offset(x) ((x).val >> 15)
-#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << 10) | ((offset) << 15) })
+#define __swp_entry(type,offset) ((swp_entry_t) { (((type) & 0x1f) << 10) | ((offset) << 15) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
#define __swp_entry_to_pte(x) ((pte_t) { (x).val })

+/* We borrow bit 7 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE (1 << 7)
+
#else

#if defined(CONFIG_XPA)

-/* Swap entries must have VALID and GLOBAL bits cleared. */
+/*
+ * 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
+ * 0 0 0 0 0 0 E P <------------------ zeroes ------------------->
+ *
+ * 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 ------------------> < type -> V G 0 0
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * _PAGE_PRESENT (P), _PAGE_VALID (V) and_PAGE_GLOBAL (G) have to remain
+ * unused.
+ */
#define __swp_type(x) (((x).val >> 4) & 0x1f)
#define __swp_offset(x) ((x).val >> 9)
-#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << 4) | ((offset) << 9) })
+#define __swp_entry(type,offset) ((swp_entry_t) { (((type) & 0x1f) << 4) | ((offset) << 9) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { (pte).pte_high })
#define __swp_entry_to_pte(x) ((pte_t) { 0, (x).val })

+/*
+ * We borrow bit 57 (bit 25 in the low PTE) to store the exclusive marker in
+ * swap PTEs.
+ */
+#define _PAGE_SWP_EXCLUSIVE (1 << 25)
+
#elif defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)

-/* Swap entries must have VALID and GLOBAL bits cleared. */
+/*
+ * 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
+ * <------------------ zeroes -------------------> E P 0 0 0 0 0 0
+ *
+ * 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 --------------------> < type -> V G
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * _PAGE_PRESENT (P), _PAGE_VALID (V) and_PAGE_GLOBAL (G) have to remain
+ * unused.
+ */
#define __swp_type(x) (((x).val >> 2) & 0x1f)
#define __swp_offset(x) ((x).val >> 7)
-#define __swp_entry(type, offset) ((swp_entry_t) { ((type) << 2) | ((offset) << 7) })
+#define __swp_entry(type, offset) ((swp_entry_t) { (((type) & 0x1f) << 2) | ((offset) << 7) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { (pte).pte_high })
#define __swp_entry_to_pte(x) ((pte_t) { 0, (x).val })

+/*
+ * We borrow bit 39 (bit 7 in the low PTE) to store the exclusive marker in swap
+ * PTEs.
+ */
+#define _PAGE_SWP_EXCLUSIVE (1 << 7)
+
#else
/*
- * Constraints:
- * _PAGE_PRESENT at bit 0
- * _PAGE_MODIFIED at bit 4
- * _PAGE_GLOBAL at bit 6
- * _PAGE_VALID at bit 7
+ * 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 --------------> < type -> 0 0 0 0 0 0 E P
+ *
+ * E is the exclusive marker that is not stored in swap entries.
+ * _PAGE_PRESENT (P), _PAGE_VALID (V) and_PAGE_GLOBAL (G) have to remain
+ * unused. The location of V and G varies.
*/
#define __swp_type(x) (((x).val >> 8) & 0x1f)
#define __swp_offset(x) ((x).val >> 13)
@@ -234,6 +295,9 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
#define __swp_entry_to_pte(x) ((pte_t) { (x).val })

+/* We borrow bit 1 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE (1 << 1)
+
#endif /* defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32) */

#endif /* defined(CONFIG_CPU_R3K_TLB) */
diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
index c6310192b654..98e24e3e7f2b 100644
--- a/arch/mips/include/asm/pgtable-64.h
+++ b/arch/mips/include/asm/pgtable-64.h
@@ -320,16 +320,31 @@ 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.
*/
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) })
#define __swp_entry_to_pte(x) ((pte_t) { (x).val })

+/* We borrow bit 23 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE (1 << 23)
+
#endif /* _ASM_PGTABLE_64_H */
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index a68c0b01d8cd..711874cee8e4 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -528,6 +528,42 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
}
#endif

+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+#if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)
+static inline int pte_swp_exclusive(pte_t pte)
+{
+ return pte.pte_low & _PAGE_SWP_EXCLUSIVE;
+}
+
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+ pte.pte_low |= _PAGE_SWP_EXCLUSIVE;
+ return pte;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+ pte.pte_low &= ~_PAGE_SWP_EXCLUSIVE;
+ return pte;
+}
+#else
+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

extern void __update_tlb(struct vm_area_struct *vma, unsigned long address,
pte_t pte);
--
2.38.1

Next message: David Hildenbrand: "[PATCH mm-unstable RFC 13/26] nios2/mm: refactor swap PTE layout"
Previous message: David Hildenbrand: "[PATCH mm-unstable RFC 11/26] microblaze/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE"
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Next in thread: David Hildenbrand: "[PATCH mm-unstable RFC 13/26] nios2/mm: refactor swap PTE layout"
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