[PATCH V4 3/3] riscv: mm: Add uffd write-protect support

[Chunyan Zhang]

Reuse PTE bit(9) to do uffd-wp tracking and make it mutually exclusive
with soft-dirty and DEVMAP which all use this PTE bit.

Additionally for tracking the uffd-wp state as a PTE swap bit,
we use swap entry pte bit(4) which is also used by swap
soft-dirty tracking.

Signed-off-by: Chunyan Zhang <zhangchunyan at iscas.ac.cn>
---
 arch/riscv/Kconfig                    |  7 +++
 arch/riscv/include/asm/pgtable-bits.h | 13 ++++++
 arch/riscv/include/asm/pgtable.h      | 66 ++++++++++++++++++++++++++-
 3 files changed, 85 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index f1460fc01cd4..aa595a5ed4b8 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -971,6 +971,13 @@ config RISCV_HAS_SOFT_DIRTY
 	help
 	  The PTE bit(9) is used for soft-dirty tracking.
 
+config RISCV_HAS_USERFAULTFD_WP
+	bool "userfaultfd write protection"
+	select HAVE_ARCH_USERFAULTFD_WP
+	depends on USERFAULTFD
+	help
+	  The PTE bit(9) is used for userfaultfd write-protected
+	  tracking.
 endchoice
 
 endmenu # "Kernel features"
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
index c6d51fe9fc6f..7de16141c049 100644
--- a/arch/riscv/include/asm/pgtable-bits.h
+++ b/arch/riscv/include/asm/pgtable-bits.h
@@ -38,6 +38,19 @@
 #define _PAGE_SWP_SOFT_DIRTY	0
 #endif /* CONFIG_MEM_SOFT_DIRTY */
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+/*
+ * CONFIG_HAVE_ARCH_USERFAULTFD_WP is mutually exclusive with
+ * HAVE_ARCH_SOFT_DIRTY so we can use the same bit for uffd-wp
+ * and soft-dirty tracking.
+ */
+#define _PAGE_UFFD_WP		(1 << 9) /* RSW: 0x2 for uffd-wp tracking */
+#define _PAGE_SWP_UFFD_WP	_PAGE_USER
+#else
+#define _PAGE_UFFD_WP		0
+#define _PAGE_SWP_UFFD_WP	0
+#endif
+
 #define _PAGE_TABLE     _PAGE_PRESENT
 
 /*
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index d41507919ef2..6ce4c9ba862a 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -417,6 +417,38 @@ static inline pte_t pte_wrprotect(pte_t pte)
 	return __pte(pte_val(pte) & ~(_PAGE_WRITE));
 }
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+static inline int pte_uffd_wp(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_UFFD_WP;
+}
+
+static inline pte_t pte_mkuffd_wp(pte_t pte)
+{
+	return pte_wrprotect(__pte(pte_val(pte) | _PAGE_UFFD_WP));
+}
+
+static inline pte_t pte_clear_uffd_wp(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~(_PAGE_UFFD_WP));
+}
+
+static inline int pte_swp_uffd_wp(pte_t pte)
+{
+	return pte_val(pte) & _PAGE_SWP_UFFD_WP;
+}
+
+static inline pte_t pte_swp_mkuffd_wp(pte_t pte)
+{
+	return pte_wrprotect(__pte(pte_val(pte) | _PAGE_SWP_UFFD_WP));
+}
+
+static inline pte_t pte_swp_clear_uffd_wp(pte_t pte)
+{
+	return __pte(pte_val(pte) & ~(_PAGE_SWP_UFFD_WP));
+}
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+
 /* static inline pte_t pte_mkread(pte_t pte) */
 
 static inline pte_t pte_mkwrite_novma(pte_t pte)
@@ -783,6 +815,38 @@ static inline pmd_t pmd_mkdevmap(pmd_t pmd)
 	return pte_pmd(pte_mkdevmap(pmd_pte(pmd)));
 }
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+static inline int pmd_uffd_wp(pmd_t pmd)
+{
+	return pte_uffd_wp(pmd_pte(pmd));
+}
+
+static inline pmd_t pmd_mkuffd_wp(pmd_t pmd)
+{
+	return pte_pmd(pte_mkuffd_wp(pmd_pte(pmd)));
+}
+
+static inline pmd_t pmd_clear_uffd_wp(pmd_t pmd)
+{
+	return pte_pmd(pte_clear_uffd_wp(pmd_pte(pmd)));
+}
+
+static inline int pmd_swp_uffd_wp(pmd_t pmd)
+{
+	return pte_swp_uffd_wp(pmd_pte(pmd));
+}
+
+static inline pmd_t pmd_swp_mkuffd_wp(pmd_t pmd)
+{
+	return pte_pmd(pte_swp_mkuffd_wp(pmd_pte(pmd)));
+}
+
+static inline pmd_t pmd_swp_clear_uffd_wp(pmd_t pmd)
+{
+	return pte_pmd(pte_swp_clear_uffd_wp(pmd_pte(pmd)));
+}
+#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_WP */
+
 #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
 static inline int pmd_soft_dirty(pmd_t pmd)
 {
@@ -907,7 +971,7 @@ extern pmd_t pmdp_collapse_flush(struct vm_area_struct *vma,
  * Format of swap PTE:
  *	bit            0:	_PAGE_PRESENT (zero)
  *	bit       1 to 3:       _PAGE_LEAF (zero)
- *	bit	       4:	_PAGE_SWP_SOFT_DIRTY
+ *	bit	       4:	_PAGE_SWP_SOFT_DIRTY or _PAGE_SWP_UFFD_WP
  *	bit            5:	_PAGE_PROT_NONE (zero)
  *	bit            6:	exclusive marker
  *	bits      7 to 11:	swap type
-- 
2.34.1