arm64: mm: swap: support THP_SWAP on hardware with MTE

Commit d0637c5 ("arm64: enable THP_SWAP for arm64") brings up
THP_SWAP on ARM64, but it doesn't enable THP_SWP on hardware with MTE as
the MTE code works with the assumption tags save/restore is always
handling a folio with only one page.

The limitation should be removed as more and more ARM64 SoCs have this
feature.  Co-existence of MTE and THP_SWAP becomes more and more
important.

This patch makes MTE tags saving support large folios, then we don't need
to split large folios into base pages for swapping out on ARM64 SoCs with
MTE any more.

arch_prepare_to_swap() should take folio rather than page as parameter
because we support THP swap-out as a whole.  It saves tags for all pages
in a large folio.

As now we are restoring tags based-on folio, in arch_swap_restore(), we
may increase some extra loops and early-exitings while refaulting a large
folio which is still in swapcache in do_swap_page().  In case a large
folio has nr pages, do_swap_page() will only set the PTE of the particular
page which is causing the page fault.  Thus do_swap_page() runs nr times,
and each time, arch_swap_restore() will loop nr times for those subpages
in the folio.  So right now the algorithmic complexity becomes O(nr^2).

Once we support mapping large folios in do_swap_page(), extra loops and
early-exitings will decrease while not being completely removed as a large
folio might get partially tagged in corner cases such as, 1.  a large
folio in swapcache can be partially unmapped, thus, MTE tags for the
unmapped pages will be invalidated; 2.  users might use mprotect() to set
MTEs on a part of a large folio.

arch_thp_swp_supported() is dropped since ARM64 MTE was the only one who
needed it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Barry Song <[email protected]>
Reviewed-by: Steven Price <[email protected]>
Acked-by: Chris Li <[email protected]>
Reviewed-by: Ryan Roberts <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: "Matthew Wilcox (Oracle)" <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Peter Collingbourne <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: "Mike Rapoport (IBM)" <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: "Aneesh Kumar K.V" <[email protected]>
Cc: Rick Edgecombe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Barry Song

arch/arm64/include/asm/pgtable.h

@@ -49,12 +49,6 @@
 	__flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1)
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
-static inline bool arch_thp_swp_supported(void)
-{
-	return !system_supports_mte();
-}
-#define arch_thp_swp_supported arch_thp_swp_supported
-
 /*
  * Outside of a few very special situations (e.g. hibernation), we always
  * use broadcast TLB invalidation instructions, therefore a spurious page
@@ -1282,12 +1276,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
 #ifdef CONFIG_ARM64_MTE
 
 #define __HAVE_ARCH_PREPARE_TO_SWAP
-static inline int arch_prepare_to_swap(struct page *page)
-{
-	if (system_supports_mte())
-		return mte_save_tags(page);
-	return 0;
-}
+extern int arch_prepare_to_swap(struct folio *folio);
 
 #define __HAVE_ARCH_SWAP_INVALIDATE
 static inline void arch_swap_invalidate_page(int type, pgoff_t offset)
@@ -1303,11 +1292,7 @@ static inline void arch_swap_invalidate_area(int type)
 }
 
 #define __HAVE_ARCH_SWAP_RESTORE
-static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
-{
-	if (system_supports_mte())
-		mte_restore_tags(entry, &folio->page);
-}
+extern void arch_swap_restore(swp_entry_t entry, struct folio *folio);
 
 #endif /* CONFIG_ARM64_MTE */
 

arch/arm64/mm/mteswap.c

@@ -68,6 +68,13 @@ void mte_invalidate_tags(int type, pgoff_t offset)
 	mte_free_tag_storage(tags);
 }
 
+static inline void __mte_invalidate_tags(struct page *page)
+{
+	swp_entry_t entry = page_swap_entry(page);
+
+	mte_invalidate_tags(swp_type(entry), swp_offset(entry));
+}
+
 void mte_invalidate_tags_area(int type)
 {
 	swp_entry_t entry = swp_entry(type, 0);
@@ -83,3 +90,41 @@ void mte_invalidate_tags_area(int type)
 	}
 	xa_unlock(&mte_pages);
 }
+
+int arch_prepare_to_swap(struct folio *folio)
+{
+	long i, nr;
+	int err;
+
+	if (!system_supports_mte())
+		return 0;
+
+	nr = folio_nr_pages(folio);
+
+	for (i = 0; i < nr; i++) {
+		err = mte_save_tags(folio_page(folio, i));
+		if (err)
+			goto out;
+	}
+	return 0;
+
+out:
+	while (i--)
+		__mte_invalidate_tags(folio_page(folio, i));
+	return err;
+}
+
+void arch_swap_restore(swp_entry_t entry, struct folio *folio)
+{
+	long i, nr;
+
+	if (!system_supports_mte())
+		return;
+
+	nr = folio_nr_pages(folio);
+
+	for (i = 0; i < nr; i++) {
+		mte_restore_tags(entry, folio_page(folio, i));
+		entry.val++;
+	}
+}

include/linux/huge_mm.h

@@ -532,16 +532,4 @@ static inline int split_folio_to_order(struct folio *folio, int new_order)
 #define split_folio_to_list(f, l) split_folio_to_list_to_order(f, l, 0)
 #define split_folio(f) split_folio_to_order(f, 0)
 
-/*
- * archs that select ARCH_WANTS_THP_SWAP but don't support THP_SWP due to
- * limitations in the implementation like arm64 MTE can override this to
- * false
- */
-#ifndef arch_thp_swp_supported
-static inline bool arch_thp_swp_supported(void)
-{
-	return true;
-}
-#endif
-
 #endif /* _LINUX_HUGE_MM_H */

include/linux/pgtable.h

@@ -1050,7 +1050,7 @@ static inline int arch_unmap_one(struct mm_struct *mm,
  * 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)
+static inline int arch_prepare_to_swap(struct folio *folio)
 {
 	return 0;
 }

mm/internal.h

@@ -76,6 +76,20 @@ static inline int folio_nr_pages_mapped(struct folio *folio)
 	return atomic_read(&folio->_nr_pages_mapped) & FOLIO_PAGES_MAPPED;
 }
 
+/*
+ * Retrieve the first entry of a folio based on a provided entry within the
+ * folio. We cannot rely on folio->swap as there is no guarantee that it has
+ * been initialized. Used for calling arch_swap_restore()
+ */
+static inline swp_entry_t folio_swap(swp_entry_t entry, struct folio *folio)
+{
+	swp_entry_t swap = {
+		.val = ALIGN_DOWN(entry.val, folio_nr_pages(folio)),
+	};
+
+	return swap;
+}
+
 static inline void *folio_raw_mapping(struct folio *folio)
 {
 	unsigned long mapping = (unsigned long)folio->mapping;

mm/memory.c

@@ -4190,7 +4190,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	 * when reading from swap. This metadata may be indexed by swap entry
 	 * so this must be called before swap_free().
 	 */
-	arch_swap_restore(entry, folio);
+	arch_swap_restore(folio_swap(entry, folio), folio);
 
 	/*
 	 * Remove the swap entry and conditionally try to free up the swapcache.

mm/page_io.c

@@ -189,7 +189,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 	 * Arch code may have to preserve more data than just the page
 	 * contents, e.g. memory tags.
 	 */
-	ret = arch_prepare_to_swap(&folio->page);
+	ret = arch_prepare_to_swap(folio);
 	if (ret) {
 		folio_mark_dirty(folio);
 		folio_unlock(folio);

mm/shmem.c

@@ -1907,7 +1907,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 	 * Some architectures may have to restore extra metadata to the
 	 * folio after reading from swap.
 	 */
-	arch_swap_restore(swap, folio);
+	arch_swap_restore(folio_swap(swap, folio), folio);
 
 	if (shmem_should_replace_folio(folio, gfp)) {
 		error = shmem_replace_folio(&folio, gfp, info, index);

mm/swap_slots.c

@@ -310,7 +310,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
 	entry.val = 0;
 
 	if (folio_test_large(folio)) {
-		if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_supported())
+		if (IS_ENABLED(CONFIG_THP_SWAP))
 			get_swap_pages(1, &entry, folio_nr_pages(folio));
 		goto out;
 	}

mm/swapfile.c

@@ -1806,7 +1806,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	 * when reading from swap. This metadata may be indexed by swap entry
 	 * so this must be called before swap_free().
 	 */
-	arch_swap_restore(entry, folio);
+	arch_swap_restore(folio_swap(entry, folio), folio);
 
 	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);