Re: [PATCH RFC v7 2/3] riscv: mm: Add soft-dirty page tracking support

[Deepak Gupta <debug@rivosinc.com>]

On Wed, Apr 09, 2025 at 05:53:19PM +0800, Chunyan Zhang wrote:
>The Svrsw60t59b extension allows to free the PTE reserved bits 60 and 59
>for software, this patch uses bit 59 for soft-dirty.
>
>To add swap PTE soft-dirty tracking, we borrow bit 3 which is available
>for swap PTEs on RISC-V systems.
>
>Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
>---
> arch/riscv/Kconfig                    |  1 +
> arch/riscv/include/asm/pgtable-bits.h | 19 +++++++
> arch/riscv/include/asm/pgtable.h      | 71 ++++++++++++++++++++++++++-
> 3 files changed, 89 insertions(+), 2 deletions(-)
>
>diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>index 332fc00243ad..652e2bbfb702 100644
>--- a/arch/riscv/Kconfig
>+++ b/arch/riscv/Kconfig
>@@ -139,6 +139,7 @@ config RISCV
> 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
> 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
> 	select HAVE_ARCH_SECCOMP_FILTER
>+	select HAVE_ARCH_SOFT_DIRTY if 64BIT && MMU && RISCV_ISA_SVRSW60T59B
> 	select HAVE_ARCH_STACKLEAK
> 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
> 	select HAVE_ARCH_TRACEHOOK
>diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
>index a8f5205cea54..a6fa871dc19e 100644
>--- a/arch/riscv/include/asm/pgtable-bits.h
>+++ b/arch/riscv/include/asm/pgtable-bits.h
>@@ -20,6 +20,25 @@
>
> #define _PAGE_SPECIAL   (1 << 8)    /* RSW: 0x1 */
> #define _PAGE_DEVMAP    (1 << 9)    /* RSW, devmap */
>+
>+#ifdef CONFIG_MEM_SOFT_DIRTY
>+
>+/* ext_svrsw60t59b: bit 59 for software dirty tracking */
>+#define _PAGE_SOFT_DIRTY						\
>+	((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ?	\
>+	 (1UL << 59) : 0)
>+/*
>+ * Bit 3 is always zero for swap entry computation, so we
>+ * can borrow it for swap page soft-dirty tracking.
>+ */
>+#define _PAGE_SWP_SOFT_DIRTY						\
>+	((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ?	\
>+	 _PAGE_EXEC : 0)
>+#else
>+#define _PAGE_SOFT_DIRTY	0
>+#define _PAGE_SWP_SOFT_DIRTY	0
>+#endif /* CONFIG_MEM_SOFT_DIRTY */
>+

Above can be done like this

+
+#ifdef CONFIG_MEM_SOFT_DIRTY && RISCV_ISA_EXT_SVRSW60T59B
+
+/* ext_svrsw60t59b: bit 59 for software dirty tracking */
+#define _PAGE_SOFT_DIRTY (1UL << 59)
+/*
+ * Bit 3 is always zero for swap entry computation, so we
+ * can borrow it for swap page soft-dirty tracking.
+ */
+#define _PAGE_SWP_SOFT_DIRTY _PAGE_EXEC
+#else
+#define _PAGE_SOFT_DIRTY       0
+#define _PAGE_SWP_SOFT_DIRTY   0
+#endif /* CONFIG_MEM_SOFT_DIRTY */

> #define _PAGE_TABLE     _PAGE_PRESENT
>
> /*
>diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>index 428e48e5f57d..14461ffe6321 100644
>--- a/arch/riscv/include/asm/pgtable.h
>+++ b/arch/riscv/include/asm/pgtable.h
>@@ -436,7 +436,7 @@ static inline pte_t pte_mkwrite_novma(pte_t pte)

Shouldn't "static inline int pte_dirty(pte_t pte)" be updated as well

static inline int pte_dirty(pte_t pte)
{
	return pte_val(pte) & (_PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}

Perhaps have a macro which includes both dirty together and then use together.


>
> static inline pte_t pte_mkdirty(pte_t pte)
> {
>-	return __pte(pte_val(pte) | _PAGE_DIRTY);
>+	return __pte(pte_val(pte) | _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
> }
>
> static inline pte_t pte_mkclean(pte_t pte)
>@@ -469,6 +469,38 @@ static inline pte_t pte_mkhuge(pte_t pte)
> 	return pte;
> }
>
>+#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
>+static inline bool pte_soft_dirty(pte_t pte)
>+{
>+	return !!(pte_val(pte) & _PAGE_SOFT_DIRTY);
>+}
>+
>+static inline pte_t pte_mksoft_dirty(pte_t pte)
>+{
>+	return __pte(pte_val(pte) | _PAGE_SOFT_DIRTY);
>+}
>+
>+static inline pte_t pte_clear_soft_dirty(pte_t pte)
>+{
>+	return __pte(pte_val(pte) & ~(_PAGE_SOFT_DIRTY));
>+}
>+
>+static inline bool pte_swp_soft_dirty(pte_t pte)
>+{
>+	return !!(pte_val(pte) & _PAGE_SWP_SOFT_DIRTY);
>+}
>+
>+static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
>+{
>+	return __pte(pte_val(pte) | _PAGE_SWP_SOFT_DIRTY);
>+}
>+
>+static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
>+{
>+	return __pte(pte_val(pte) & ~(_PAGE_SWP_SOFT_DIRTY));
>+}
>+#endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
>+
> #ifdef CONFIG_RISCV_ISA_SVNAPOT
> #define pte_leaf_size(pte)	(pte_napot(pte) ?				\
> 					napot_cont_size(napot_cont_order(pte)) :\
>@@ -821,6 +853,40 @@ static inline pud_t pud_mkspecial(pud_t pud)
> }
> #endif
>
>+#ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY
>+static inline bool pmd_soft_dirty(pmd_t pmd)
>+{
>+	return pte_soft_dirty(pmd_pte(pmd));
>+}
>+
>+static inline pmd_t pmd_mksoft_dirty(pmd_t pmd)
>+{
>+	return pte_pmd(pte_mksoft_dirty(pmd_pte(pmd)));
>+}
>+
>+static inline pmd_t pmd_clear_soft_dirty(pmd_t pmd)
>+{
>+	return pte_pmd(pte_clear_soft_dirty(pmd_pte(pmd)));
>+}
>+
>+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
>+static inline bool pmd_swp_soft_dirty(pmd_t pmd)
>+{
>+	return pte_swp_soft_dirty(pmd_pte(pmd));
>+}
>+
>+static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
>+{
>+	return pte_pmd(pte_swp_mksoft_dirty(pmd_pte(pmd)));
>+}
>+
>+static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
>+{
>+	return pte_pmd(pte_swp_clear_soft_dirty(pmd_pte(pmd)));
>+}
>+#endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */
>+#endif /* CONFIG_HAVE_ARCH_SOFT_DIRTY */
>+
> static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
> 				pmd_t *pmdp, pmd_t pmd)
> {
>@@ -910,7 +976,8 @@ 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       1 to 2:	(zero)
>+ *	bit            3:	_PAGE_SWP_SOFT_DIRTY
>  *	bit            5:	_PAGE_PROT_NONE (zero)
>  *	bit            6:	exclusive marker
>  *	bits      7 to 11:	swap type
>-- 
>2.34.1
>

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