[PATCH v3 2/3] mm: Call arch_swap_restore() from unuse_pte()

[Peter Collingbourne <pcc@google.com>]

We would like to move away from requiring architectures to restore
metadata from swap in the set_pte_at() implementation, as this is not only
error-prone but adds complexity to the arch-specific code. This requires
us to call arch_swap_restore() before calling swap_free() whenever pages
are restored from swap. We are currently doing so everywhere except in
unuse_pte(); do so there as well.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I68276653e612d64cde271ce1b5a99ae05d6bbc4f
---
 mm/swapfile.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 274bbf797480..e9843fadecd6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1794,6 +1794,13 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		goto setpte;
 	}
 
+	/*
+	 * Some architectures may have to restore extra metadata to the page
+	 * when reading from swap. This metadata may be indexed by swap entry
+	 * so this must be called before swap_free().
+	 */
+	arch_swap_restore(entry, page_folio(page));
+
 	/* See do_swap_page() */
 	BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
 	BUG_ON(PageAnon(page) && PageAnonExclusive(page));
-- 
2.40.1.606.ga4b1b128d6-goog