Subject: [PATCH v2 3/8] x86/pgtable: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE

From: David Hildenbrand <[email-masked]>
Date: Tue, 29 Mar 2022 18:43:24 +0200

Let's use bit 3 to remember PG_anon_exclusive in swap ptes.

Signed-off-by: David Hildenbrand <[email-masked]>
---
 arch/x86/include/asm/pgtable.h       | 16 ++++++++++++++++
 arch/x86/include/asm/pgtable_64.h    |  4 +++-
 arch/x86/include/asm/pgtable_types.h |  5 +++++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 62ab07e24aef..e42e668153e9 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1292,6 +1292,22 @@ static inline void update_mmu_cache_pud(struct vm_area_struct *vma,
 {
 }
 
+#define __HAVE_ARCH_PTE_SWP_EXCLUSIVE
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+	return pte_set_flags(pte, _PAGE_SWP_EXCLUSIVE);
+}
+
+static inline int pte_swp_exclusive(pte_t pte)
+{
+	return pte_flags(pte) & _PAGE_SWP_EXCLUSIVE;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+	return pte_clear_flags(pte, _PAGE_SWP_EXCLUSIVE);
+}
+
 #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
 static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
 {
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 56d0399a0cd1..e479491da8d5 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -186,7 +186,7 @@ static inline void native_pgd_clear(pgd_t *pgd)
  *
  * |     ...            | 11| 10|  9|8|7|6|5| 4| 3|2| 1|0| <- bit number
  * |     ...            |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit names
- * | TYPE (59-63) | ~OFFSET (9-58)  |0|0|X|X| X| X|F|SD|0| <- swp entry
+ * | TYPE (59-63) | ~OFFSET (9-58)  |0|0|X|X| X| E|F|SD|0| <- swp entry
  *
  * G (8) is aliased and used as a PROT_NONE indicator for
  * !present ptes.  We need to start storing swap entries above
@@ -203,6 +203,8 @@ static inline void native_pgd_clear(pgd_t *pgd)
  * F (2) in swp entry is used to record when a pagetable is
  * writeprotected by userfaultfd WP support.
  *
+ * E (3) in swp entry is used to rememeber PG_anon_exclusive.
+ *
  * Bit 7 in swp entry should be 0 because pmd_present checks not only P,
  * but also L and G.
  *
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 40497a9020c6..54a8f370046d 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -83,6 +83,11 @@
 #define _PAGE_SOFT_DIRTY	(_AT(pteval_t, 0))
 #endif
 
+/*
+ * We borrow bit 3 to remember PG_anon_exclusive.
+ */
+#define _PAGE_SWP_EXCLUSIVE	_PAGE_PWT
+
 /*
  * Tracking soft dirty bit when a page goes to a swap is tricky.
  * We need a bit which can be stored in pte _and_ not conflict
-- 
2.35.1