[RFC 1/4] arm64/mm: Add SW and HW dirty state helpers

[Anshuman Khandual <anshuman.khandual@xxxxxxx>]

This factors out low level SW and HW state changes i.e make and clear into
separate helpers making them explicit improving readability. This also adds
pte_rdonly() helper as well. No functional change is intended.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
---
 arch/arm64/include/asm/pgtable.h | 52 ++++++++++++++++++++++++++------
 1 file changed, 42 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0bd18de9fd97..fb03be697819 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -103,6 +103,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
 #define pte_young(pte)		(!!(pte_val(pte) & PTE_AF))
 #define pte_special(pte)	(!!(pte_val(pte) & PTE_SPECIAL))
 #define pte_write(pte)		(!!(pte_val(pte) & PTE_WRITE))
+#define pte_rdonly(pte)		(!!(pte_val(pte) & PTE_RDONLY))
 #define pte_user(pte)		(!!(pte_val(pte) & PTE_USER))
 #define pte_user_exec(pte)	(!(pte_val(pte) & PTE_UXN))
 #define pte_cont(pte)		(!!(pte_val(pte) & PTE_CONT))
@@ -120,7 +121,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
 	(__boundary - 1 < (end) - 1) ? __boundary : (end);			\
 })
 
-#define pte_hw_dirty(pte)	(pte_write(pte) && !(pte_val(pte) & PTE_RDONLY))
+#define pte_hw_dirty(pte)	(pte_write(pte) && !pte_rdonly(pte))
 #define pte_sw_dirty(pte)	(!!(pte_val(pte) & PTE_DIRTY))
 #define pte_dirty(pte)		(pte_sw_dirty(pte) || pte_hw_dirty(pte))
 
@@ -174,6 +175,39 @@ static inline pmd_t clear_pmd_bit(pmd_t pmd, pgprot_t prot)
 	return pmd;
 }
 
+static inline pte_t pte_hw_mkdirty(pte_t pte)
+{
+	if (pte_write(pte))
+		pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
+
+	return pte;
+}
+
+static inline pte_t pte_sw_mkdirty(pte_t pte)
+{
+	return set_pte_bit(pte, __pgprot(PTE_DIRTY));
+}
+
+static inline __always_unused pte_t pte_hw_clr_dirty(pte_t pte)
+{
+	return set_pte_bit(pte, __pgprot(PTE_RDONLY));
+}
+
+static inline pte_t pte_sw_clr_dirty(pte_t pte)
+{
+	pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY));
+
+	/*
+	 * Clearing the software dirty state requires clearing
+	 * the PTE_DIRTY bit along with setting the PTE_RDONLY
+	 * ensuring a page fault on subsequent write access.
+	 *
+	 * NOTE: Setting the PTE_RDONLY (as a coincident) also
+	 * implies clearing the HW dirty state.
+	 */
+	return set_pte_bit(pte, __pgprot(PTE_RDONLY));
+}
+
 static inline pmd_t set_pmd_bit(pmd_t pmd, pgprot_t prot)
 {
 	pmd_val(pmd) |= pgprot_val(prot);
@@ -189,19 +223,17 @@ static inline pte_t pte_mkwrite(pte_t pte)
 
 static inline pte_t pte_mkclean(pte_t pte)
 {
-	pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY));
-	pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
-
-	return pte;
+	/*
+	 * Subsequent call to pte_hw_clr_dirty() is not required
+	 * because pte_sw_clr_dirty() in turn does that as well.
+	 */
+	return pte_sw_clr_dirty(pte);
 }
 
 static inline pte_t pte_mkdirty(pte_t pte)
 {
-	pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
-
-	if (pte_write(pte))
-		pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
-
+	pte = pte_sw_mkdirty(pte);
+	pte = pte_hw_mkdirty(pte);
 	return pte;
 }
 
-- 
2.30.2