[RFC, PATCH 09/22] mm, rmap: Add arch-specific field into anon_vma

[Kirill A. Shutemov]

MKTME enabling requires a way to find out which encryption KeyID has to
be used to access the page. There's not enough space in struct page to
store this information.

As a way out we can store it in anon_vma for the page: all pages in the
same anon_vma tree will be encrypted with the same KeyID.

This patch adds arch-specific field into anon_vma. For x86 it will be
used to store KeyID.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/rmap.h |  6 ++++++
 mm/rmap.c            | 15 ++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 988d176472df..54c7ea330827 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -12,6 +12,10 @@
 #include <linux/memcontrol.h>
 #include <linux/highmem.h>
 
+#ifndef arch_anon_vma
+struct arch_anon_vma {};
+#endif
+
 /*
  * The anon_vma heads a list of private "related" vmas, to scan if
  * an anonymous page pointing to this anon_vma needs to be unmapped:
@@ -59,6 +63,8 @@ struct anon_vma {
 
 	/* Interval tree of private "related" vmas */
 	struct rb_root_cached rb_root;
+
+	struct arch_anon_vma arch_anon_vma;
 };
 
 /*
diff --git a/mm/rmap.c b/mm/rmap.c
index 47db27f8049e..c0470a69a4c9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -74,7 +74,14 @@
 static struct kmem_cache *anon_vma_cachep;
 static struct kmem_cache *anon_vma_chain_cachep;
 
-static inline struct anon_vma *anon_vma_alloc(void)
+#ifndef arch_anon_vma_init
+static inline void arch_anon_vma_init(struct anon_vma *anon_vma,
+		struct vm_area_struct *vma)
+{
+}
+#endif
+
+static inline struct anon_vma *anon_vma_alloc(struct vm_area_struct *vma)
 {
 	struct anon_vma *anon_vma;
 
@@ -88,6 +95,8 @@ static inline struct anon_vma *anon_vma_alloc(void)
 		 * from fork, the root will be reset to the parents anon_vma.
 		 */
 		anon_vma->root = anon_vma;
+
+		arch_anon_vma_init(anon_vma, vma);
 	}
 
 	return anon_vma;
@@ -186,7 +195,7 @@ int __anon_vma_prepare(struct vm_area_struct *vma)
 	anon_vma = find_mergeable_anon_vma(vma);
 	allocated = NULL;
 	if (!anon_vma) {
-		anon_vma = anon_vma_alloc();
+		anon_vma = anon_vma_alloc(vma);
 		if (unlikely(!anon_vma))
 			goto out_enomem_free_avc;
 		allocated = anon_vma;
@@ -337,7 +346,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
 		return 0;
 
 	/* Then add our own anon_vma. */
-	anon_vma = anon_vma_alloc();
+	anon_vma = anon_vma_alloc(vma);
 	if (!anon_vma)
 		goto out_error;
 	avc = anon_vma_chain_alloc(GFP_KERNEL);
-- 
2.16.1