[PATCH v5 21/25] mm: Add arch hooks for saving/restoring tags

[Catalin Marinas <catalin.marinas@xxxxxxx>]

From: Steven Price <steven.price@xxxxxxx>

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_tags()

Signed-off-by: Steven Price <steven.price@xxxxxxx>
[catalin.marinas@xxxxxxx: add unlock_page() on the error path]
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

Notes:
    New in v4.

 include/linux/pgtable.h | 23 +++++++++++++++++++++++
 mm/page_io.c            | 10 ++++++++++
 mm/shmem.c              |  6 ++++++
 mm/swapfile.c           |  2 ++
 4 files changed, 41 insertions(+)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 56c1e8eb7bb0..5053d84ece04 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -631,6 +631,29 @@ static inline int arch_unmap_one(struct mm_struct *mm,
 }
 #endif
 
+#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_TAGS
+static inline void arch_swap_restore_tags(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
diff --git a/mm/page_io.c b/mm/page_io.c
index e8726f3e3820..9f3835161002 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -252,6 +252,16 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		unlock_page(page);
 		goto out;
 	}
+	/*
+	 * Arch code may have to preserve more data than just the page
+	 * contents, e.g. memory tags.
+	 */
+	ret = arch_prepare_to_swap(page);
+	if (ret) {
+		set_page_dirty(page);
+		unlock_page(page);
+		goto out;
+	}
 	if (frontswap_store(page) == 0) {
 		set_page_writeback(page);
 		unlock_page(page);
diff --git a/mm/shmem.c b/mm/shmem.c
index dacee627dae6..6cf6a1ed3d1c 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1673,6 +1673,12 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index,
 	}
 	wait_on_page_writeback(page);
 
+	/*
+	 * Some architectures may have to restore extra metadata to the
+	 * physical page after reading from swap.
+	 */
+	arch_swap_restore_tags(swap, page);
+
 	if (shmem_should_replace_page(page, gfp)) {
 		error = shmem_replace_page(&page, gfp, info, index);
 		if (error)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 987276c557d1..b7a3ed45e606 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -716,6 +716,7 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 	else
 		swap_slot_free_notify = NULL;
 	while (offset <= end) {
+		arch_swap_invalidate_page(si->type, offset);
 		frontswap_invalidate_page(si->type, offset);
 		if (swap_slot_free_notify)
 			swap_slot_free_notify(si->bdev, offset);
@@ -2675,6 +2676,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	frontswap_map = frontswap_map_get(p);
 	spin_unlock(&p->lock);
 	spin_unlock(&swap_lock);
+	arch_swap_invalidate_area(p->type);
 	frontswap_invalidate_area(p->type);
 	frontswap_map_set(p, NULL);
 	mutex_unlock(&swapon_mutex);