[PATCH V13 5/6] riscv: mm: Add userfaultfd write-protect support

[Chunyan Zhang <zhangchunyan@iscas.ac.cn>]

The Svrsw60t59b extension allows to free the PTE reserved bits 60 and 59
for software, this patch uses bit 60 for uffd-wp tracking

Additionally for tracking the uffd-wp state as a PTE swap bit, we borrow
bit 4 which is not involved into swap entry computation.

Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
---
 arch/riscv/Kconfig                    |  1 +
 arch/riscv/include/asm/pgtable-bits.h | 18 +++++++
 arch/riscv/include/asm/pgtable.h      | 68 +++++++++++++++++++++++++++
 3 files changed, 87 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 53b73e4bdf3f..f928768bb14a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -147,6 +147,7 @@ config RISCV
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if 64BIT && MMU
 	select HAVE_ARCH_USERFAULTFD_MINOR if 64BIT && USERFAULTFD
+	select HAVE_ARCH_USERFAULTFD_WP if 64BIT && MMU && USERFAULTFD && RISCV_ISA_SVRSW60T59B
 	select HAVE_ARCH_VMAP_STACK if MMU && 64BIT
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_CONTEXT_TRACKING_USER
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
index f3bac2bbc157..b422d9691e60 100644
--- a/arch/riscv/include/asm/pgtable-bits.h
+++ b/arch/riscv/include/asm/pgtable-bits.h
@@ -38,6 +38,24 @@
 #define _PAGE_SWP_SOFT_DIRTY	0
 #endif /* CONFIG_MEM_SOFT_DIRTY */
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+
+/* ext_svrsw60t59b: Bit(60) for uffd-wp tracking */
+#define _PAGE_UFFD_WP							\
+	((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ?	\
+	 (1UL << 60) : 0)
+/*
+ * Bit 4 is not involved into swap entry computation, so we
+ * can borrow it for swap page uffd-wp tracking.
+ */
+#define _PAGE_SWP_UFFD_WP						\
+	((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ?	\
+	 _PAGE_USER : 0)
+#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 d7fe0f78107b..71e84c114dc4 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -416,6 +416,41 @@ static inline pte_t pte_wrprotect(pte_t pte)
 	return __pte(pte_val(pte) & ~(_PAGE_WRITE));
 }
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+#define pgtable_supports_uffd_wp()	\
+	riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)
+
+static inline bool 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 bool 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(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)
@@ -838,6 +873,38 @@ static inline pud_t pud_mkspecial(pud_t pud)
 }
 #endif
 
+#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
+static inline bool 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 bool 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 bool pmd_soft_dirty(pmd_t pmd)
 {
@@ -1066,6 +1133,7 @@ static inline pud_t pud_modify(pud_t pud, pgprot_t newprot)
  *	bit            0:	_PAGE_PRESENT (zero)
  *	bit       1 to 2:	(zero)
  *	bit            3:	_PAGE_SWP_SOFT_DIRTY
+ *	bit            4:	_PAGE_SWP_UFFD_WP
  *	bit            5:	_PAGE_PROT_NONE (zero)
  *	bit            6:	exclusive marker
  *	bits      7 to 11:	swap type
-- 
2.34.1