[RFC PATCH v3 06/10] mm/mshare: Add vm flag for shared PTEs

[Anthony Yznaga <anthony.yznaga@oracle.com>]

From: Khalid Aziz <khalid@kernel.org>

Add a bit to vm_flags to indicate a vma shares PTEs with others. Add
a function to determine if a vma shares PTEs by checking this flag.
This is to be used to find the shared page table entries on page fault
for vmas sharing PTEs.

Signed-off-by: Khalid Aziz <khalid@kernel.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 include/linux/mm.h             | 7 +++++++
 include/trace/events/mmflags.h | 3 +++
 mm/internal.h                  | 5 +++++
 3 files changed, 15 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6549d0979b28..3aa0b3322284 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -413,6 +413,13 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_DROPPABLE		VM_NONE
 #endif
 
+#ifdef CONFIG_64BIT
+#define VM_SHARED_PT_BIT	41
+#define VM_SHARED_PT		BIT(VM_SHARED_PT_BIT)
+#else
+#define VM_SHARED_PT		VM_NONE
+#endif
+
 #ifdef CONFIG_64BIT
 /* VM is sealed, in vm_flags */
 #define VM_SEALED	_BITUL(63)
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index b63d211bd141..e1ae1e60d086 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -167,8 +167,10 @@ IF_HAVE_PG_ARCH_X(arch_3)
 
 #ifdef CONFIG_64BIT
 # define IF_HAVE_VM_DROPPABLE(flag, name) {flag, name},
+# define IF_HAVE_VM_SHARED_PT(flag, name) {flag, name},
 #else
 # define IF_HAVE_VM_DROPPABLE(flag, name)
+# define IF_HAVE_VM_SHARED_PT(flag, name)
 #endif
 
 #define __def_vmaflag_names						\
@@ -204,6 +206,7 @@ IF_HAVE_VM_SOFTDIRTY(VM_SOFTDIRTY,	"softdirty"	)		\
 	{VM_HUGEPAGE,			"hugepage"	},		\
 	{VM_NOHUGEPAGE,			"nohugepage"	},		\
 IF_HAVE_VM_DROPPABLE(VM_DROPPABLE,	"droppable"	)		\
+IF_HAVE_VM_SHARED_PT(VM_SHARED_PT,	"sharedpt"	)		\
 	{VM_MERGEABLE,			"mergeable"	}		\
 
 #define show_vma_flags(flags)						\
diff --git a/mm/internal.h b/mm/internal.h
index b4d86436565b..8005d5956b6e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1578,4 +1578,9 @@ void unlink_file_vma_batch_init(struct unlink_vma_file_batch *);
 void unlink_file_vma_batch_add(struct unlink_vma_file_batch *, struct vm_area_struct *);
 void unlink_file_vma_batch_final(struct unlink_vma_file_batch *);
 
+static inline bool vma_is_shared(const struct vm_area_struct *vma)
+{
+	return VM_SHARED_PT && (vma->vm_flags & VM_SHARED_PT);
+}
+
 #endif	/* __MM_INTERNAL_H */
-- 
2.43.5