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>

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index e8cbc2e795d530099fe135a51b9e1fcd63e03386..dc3b74129fbcce8f44dfeb19a7f62dc1d5e09c4f 100644 (file)
--- 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

diff --git a/mm/page_io.c b/mm/page_io.c
index e485a6e8a6cddb22c6e71b1280a1b35cc1b725aa..4ca28aad0d9461b3fcd5b46d3deb92fcea525765 100644 (file)
--- 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 ec94f4c7851e4461fa2c6c1b92f8b24c34ab134a..e57d3314dc4bcfc11e43e5674e5098cda9c65976 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1734,6 +1734,12 @@ 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(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 12f59e641b5e295cf3c97eb0e8bed962af1e4d35..4b1d1a04e3271e5919c98d385e0ea8000cb8f659 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -717,6 +717,7 @@ 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);
@@ -2682,6 +2683,7 @@ 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);