From: Alistair Popple <alistair@popple.id.au>
Date: Fri, 4 Sep 2020 16:36:01 -0700
Subject: mm/rmap: fixup copying of soft dirty and uffd ptes
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Git-commit: ad7df764b7e1c7dc64e016da7ada2e3e1bb90700
Patch-mainline: v5.9-rc4
References: git-fixes (mm/rmap)

[ vbabka@suse.cz SLE15-SP1 backport: we don't have uffd ptes here, so only
  fix the soft-dirty part ]

During memory migration a pte is temporarily replaced with a migration
swap pte.  Some pte bits from the existing mapping such as the soft-dirty
and uffd write-protect bits are preserved by copying these to the
temporary migration swap pte.

However these bits are not stored at the same location for swap and
non-swap ptes.  Therefore testing these bits requires using the
appropriate helper function for the given pte type.

Unfortunately several code locations were found where the wrong helper
function is being used to test soft_dirty and uffd_wp bits which leads to
them getting incorrectly set or cleared during page-migration.

Fix these by using the correct tests based on pte type.

Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration")
Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration")
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Alistair Popple <alistair@popple.id.au>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200825064232.10023-2-alistair@popple.id.au
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/migrate.c |    9 +++++++--
 mm/rmap.c    |    6 +++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2274,8 +2274,13 @@ again:
 			/* Setup special migration page table entry */
 			entry = make_migration_entry(page, pte_write(pte));
 			swp_pte = swp_entry_to_pte(entry);
-			if (pte_soft_dirty(pte))
-				swp_pte = pte_swp_mksoft_dirty(swp_pte);
+			if (pte_present(pte)) {
+				if (pte_soft_dirty(pte))
+					swp_pte = pte_swp_mksoft_dirty(swp_pte);
+			} else {
+				if (pte_swp_soft_dirty(pte))
+					swp_pte = pte_swp_mksoft_dirty(swp_pte);
+			}
 			set_pte_at(mm, addr, ptep, swp_pte);
 
 			/*
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1449,7 +1449,11 @@ static bool try_to_unmap_one(struct page
 			 */
 			entry = make_migration_entry(page, 0);
 			swp_pte = swp_entry_to_pte(entry);
-			if (pte_soft_dirty(pteval))
+			/*
+			 * pteval maps a zone device page and is therefore
+			 * a swap pte.
+			 */
+			if (pte_swp_soft_dirty(pteval))
 				swp_pte = pte_swp_mksoft_dirty(swp_pte);
 			set_pte_at(mm, pvmw.address, pvmw.pte, swp_pte);
 			/*