diff mbox series

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

Message ID 20221206144730.163732-13-david@redhat.com (mailing list archive)
State New, archived
Headers show
Series mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with swap PTEs | expand

Commit Message

David Hildenbrand Dec. 6, 2022, 2:47 p.m. UTC 
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@alpha.franken.de>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 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 mbox series

Patch

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);