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Subject[RFC, PATCH 13/22] mm, rmap: Free encrypted pages once mapcount drops to zero
Date
Freeing encrypted pages may require special treatment such as flush
cache to avoid aliasing.

Anonymous pages cannot be mapped back once the last mapcount is gone.
That's a good place to add hook to free encrypted page. At later point
we may not have valid anon_vma around to get KeyID.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
include/linux/mm.h | 1 +
mm/rmap.c | 34 ++++++++++++++++++++++++++++++++--
2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7a4285f09c99..7ab5e39e3195 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1981,6 +1981,7 @@ extern void mem_init_print_info(const char *str);
extern void reserve_bootmem_region(phys_addr_t start, phys_addr_t end);

extern void prep_encrypt_page(struct page *page, gfp_t gfp, unsigned int order);
+extern void free_encrypt_page(struct page *page, int keyid, unsigned int order);

/* Free the reserved page into the buddy system, so it gets managed. */
static inline void __free_reserved_page(struct page *page)
diff --git a/mm/rmap.c b/mm/rmap.c
index c0470a69a4c9..4bff992fc106 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -81,6 +81,21 @@ static inline void arch_anon_vma_init(struct anon_vma *anon_vma,
}
#endif

+#ifndef anon_vma_encrypted
+static inline bool anon_vma_encrypted(struct anon_vma *anon_vma)
+{
+ return false;
+}
+#endif
+
+#ifndef anon_vma_keyid
+static inline int anon_vma_keyid(struct anon_vma *anon_vma)
+{
+ BUILD_BUG();
+ return 0;
+}
+#endif
+
static inline struct anon_vma *anon_vma_alloc(struct vm_area_struct *vma)
{
struct anon_vma *anon_vma;
@@ -1258,6 +1273,7 @@ static void page_remove_file_rmap(struct page *page, bool compound)

static void page_remove_anon_compound_rmap(struct page *page)
{
+ struct anon_vma *anon_vma;
int i, nr;

if (!atomic_add_negative(-1, compound_mapcount_ptr(page)))
@@ -1292,6 +1308,12 @@ static void page_remove_anon_compound_rmap(struct page *page)
__mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
deferred_split_huge_page(page);
}
+
+ anon_vma = page_anon_vma(page);
+ if (anon_vma_encrypted(anon_vma)) {
+ int keyid = anon_vma_keyid(anon_vma);
+ free_encrypt_page(page, keyid, compound_order(page));
+ }
}

/**
@@ -1303,6 +1325,9 @@ static void page_remove_anon_compound_rmap(struct page *page)
*/
void page_remove_rmap(struct page *page, bool compound)
{
+ struct page *head;
+ struct anon_vma *anon_vma;
+
if (!PageAnon(page))
return page_remove_file_rmap(page, compound);

@@ -1323,8 +1348,13 @@ void page_remove_rmap(struct page *page, bool compound)
if (unlikely(PageMlocked(page)))
clear_page_mlock(page);

- if (PageTransCompound(page))
- deferred_split_huge_page(compound_head(page));
+ head = compound_head(page);
+ if (PageTransHuge(head))
+ deferred_split_huge_page(head);
+
+ anon_vma = page_anon_vma(head);
+ if (anon_vma_encrypted(anon_vma))
+ free_encrypt_page(page, anon_vma_keyid(anon_vma), 0);

/*
* It would be tidy to reset the PageAnon mapping here,
--
2.16.1
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