mm: Add arch hooks for saving/restoring tags

Arm's Memory Tagging Extension (MTE) adds some metadata (tags) to
every physical page, when swapping pages out to disk it is necessary to
save these tags, and later restore them when reading the pages back.

Add some hooks along with dummy implementations to enable the
arch code to handle this.

Three new hooks are added to the swap code:
 * arch_prepare_to_swap() and
 * arch_swap_invalidate_page() / arch_swap_invalidate_area().
One new hook is added to shmem:
 * arch_swap_restore()

Signed-off-by: Steven Price <steven.price@arm.com>
[catalin.marinas@arm.com: add unlock_page() on the error path]
[catalin.marinas@arm.com: dropped the _tags suffix]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index e8cbc2e795d5..dc3b74129fbc 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -633,6 +633,34 @@ static inline int arch_unmap_one(struct mm_struct *mm,
 }
 #endif
 
+/*
+ * Allow architectures to preserve additional metadata associated with
+ * swapped-out pages. The corresponding __HAVE_ARCH_SWAP_* macros and function
+ * prototypes must be defined in the arch-specific asm/pgtable.h file.
+ */
+#ifndef __HAVE_ARCH_PREPARE_TO_SWAP
+static inline int arch_prepare_to_swap(struct page *page)
+{
+	return 0;
+}
+#endif
+
+#ifndef __HAVE_ARCH_SWAP_INVALIDATE
+static inline void arch_swap_invalidate_page(int type, pgoff_t offset)
+{
+}
+
+static inline void arch_swap_invalidate_area(int type)
+{
+}
+#endif
+
+#ifndef __HAVE_ARCH_SWAP_RESTORE
+static inline void arch_swap_restore(swp_entry_t entry, struct page *page)
+{
+}
+#endif
+
 #ifndef __HAVE_ARCH_PGD_OFFSET_GATE
 #define pgd_offset_gate(mm, addr)	pgd_offset(mm, addr)
 #endif