[RFC] arm64: properly define SOFT_DIRTY for arm64

[Nico Pache]

ARM64 has a soft-dirty bit (software dirty) but never properly defines
CONFIG_ARCH_HAS_SOFT_DIRTY or its necessary functions. This patch
introduces the ability to set/clear the soft dirty bit in a similar
manner as the other arches that utilize it.

However, we must be careful... there are cases where the DBM bit is not
available and the software dirty bit plays a essential role in determining
whether or not a page is dirty. In these cases we must not allow the
user to clear the software dirty bit. We can test for these cases by
utilizing the arch_faults_on_old_pte() function which test the availability
of DBM.

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Gerald Schaefer <gerald.schaefer at linux.ibm.com>
Cc: Liu Shixin <liushixin2 at huawei.com>
Cc: Will Deacon <will at kernel.org>
Cc: Yu Zhao <yuzhao at google.com>
Signed-off-by: Nico Pache <npache at redhat.com>
---
 arch/arm64/Kconfig               |  1 +
 arch/arm64/include/asm/pgtable.h | 77 +++++++++++++++++++++++++++++++-
 2 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 891ab530a665..4de491627f49 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -173,6 +173,7 @@ config ARM64
 	select HAVE_ARCH_PREL32_RELOCATIONS
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_SOFT_DIRTY
 	select HAVE_ARCH_STACKLEAK
 	select HAVE_ARCH_THREAD_STRUCT_WHITELIST
 	select HAVE_ARCH_TRACEHOOK
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0bd18de9fd97..a0a15ffa2417 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -121,8 +121,9 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
 })
 
 #define pte_hw_dirty(pte)	(pte_write(pte) && !(pte_val(pte) & PTE_RDONLY))
-#define pte_sw_dirty(pte)	(!!(pte_val(pte) & PTE_DIRTY))
-#define pte_dirty(pte)		(pte_sw_dirty(pte) || pte_hw_dirty(pte))
+#define pte_soft_dirty(pte)	(!!(pte_val(pte) & PTE_DIRTY))
+#define pte_dirty(pte)		(pte_soft_dirty(pte) || pte_hw_dirty(pte))
+#define pte_swp_soft_dirty(pte)	pte_soft_dirty(pte)
 
 #define pte_valid(pte)		(!!(pte_val(pte) & PTE_VALID))
 /*
@@ -1096,6 +1097,78 @@ static inline bool pud_sect_supported(void)
 	return PAGE_SIZE == SZ_4K;
 }
 
+#ifdef CONFIG_ARM64_HW_AFDBM
+/*
+ * if we have the DBM bit we can utilize the software dirty bit as
+ * a mechanism to introduce the soft_dirty functionality; however, without
+ * it this bit is crucial to determining if a entry is dirty and we cannot
+ * clear it via software. DBM can also be disabled or broken on some early
+ * armv8 devices, so check its availability before modifying it.
+ */
+static inline pte_t pte_clear_soft_dirty(pte_t pte)
+{
+	if (arch_faults_on_old_pte())
+		return pte;
+
+	return clear_pte_bit(pte, __pgprot(PTE_DIRTY));
+}
+
+static inline pte_t pte_mksoft_dirty(pte_t pte)
+{
+	if (arch_faults_on_old_pte())
+		return pte;
+
+	return set_pte_bit(pte, __pgprot(PTE_DIRTY));
+}
+
+static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
+{
+	if (arch_faults_on_old_pte())
+		return pte;
+
+	return clear_pte_bit(pte, __pgprot(PTE_DIRTY));
+}
+
+static inline pte_t pte_swp_mksoft_dirty(pte_t pte)
+{
+	if (arch_faults_on_old_pte())
+		return pte;
+
+	return set_pte_bit(pte, __pgprot(PTE_DIRTY));
+}
+
+static inline int pmd_soft_dirty(pmd_t pmd)
+{
+	return pte_soft_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)));
+}
+
+static inline pmd_t pmd_mksoft_dirty(pmd_t pmd)
+{
+	return pte_pmd(pte_mksoft_dirty(pmd_pte(pmd)));
+}
+
+#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
+static inline int pmd_swp_soft_dirty(pmd_t pmd)
+{
+	return pmd_soft_dirty(pmd);
+}
+
+static inline pmd_t pmd_swp_clear_soft_dirty(pmd_t pmd)
+{
+	return pmd_clear_soft_dirty(pmd);
+}
+
+static inline pmd_t pmd_swp_mksoft_dirty(pmd_t pmd)
+{
+	return pmd_mksoft_dirty(pmd);
+}
+#endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */
+#endif /* CONFIG_ARM64_HW_AFDBM */
 
 #define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
 #define ptep_modify_prot_start ptep_modify_prot_start
-- 
2.41.0