[merged mm-hotfixes-stable] mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: mm/memory: fix missing pte marker for !page on pte zaps
has been removed from the -mm tree.  Its filename was
     mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm/memory: fix missing pte marker for !page on pte zaps
Date: Wed, 13 Mar 2024 17:31:07 -0400

Commit 0cf18e839f64 of large folio zap work broke uffd-wp.  Now mm's uffd
unit test "wp-unpopulated" will trigger this WARN_ON_ONCE().

The WARN_ON_ONCE() asserts that an VMA cannot be registered with
userfaultfd-wp if it contains a !normal page, but it's actually possible. 
One example is an anonymous vma, register with uffd-wp, read anything will
install a zero page.  Then when zap on it, this should trigger.

What's more, removing that WARN_ON_ONCE may not be enough either, because
we should also not rely on "whether it's a normal page" to decide whether
pte marker is needed.  For example, one can register wr-protect over some
DAX regions to track writes when UFFD_FEATURE_WP_ASYNC enabled, in which
case it can have page==NULL for a devmap but we may want to keep the
marker around.

Link: https://lkml.kernel.org/r/20240313213107.235067-1-peterx@redhat.com
Fixes: 0cf18e839f64 ("mm/memory: handle !page case in zap_present_pte() separately")
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/memory.c~mm-memory-fix-missing-pte-marker-for-page-on-pte-zaps
+++ a/mm/memory.c
@@ -1536,7 +1536,9 @@ static inline int zap_present_ptes(struc
 		ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
 		arch_check_zapped_pte(vma, ptent);
 		tlb_remove_tlb_entry(tlb, pte, addr);
-		VM_WARN_ON_ONCE(userfaultfd_wp(vma));
+		if (userfaultfd_pte_wp(vma, ptent))
+			zap_install_uffd_wp_if_needed(vma, addr, pte, 1,
+						      details, ptent);
 		ksm_might_unmap_zero_page(mm, ptent);
 		return 1;
 	}
_

Patches currently in -mm which might be from peterx@redhat.com are

mm-hmm-process-pud-swap-entry-without-pud_huge.patch
mm-gup-cache-p4d-in-follow_p4d_mask.patch
mm-gup-check-p4d-presence-before-going-on.patch
mm-x86-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-sparc-change-pxd_huge-behavior-to-exclude-swap-entries.patch
mm-arm-use-macros-to-define-pmd-pud-helpers.patch
mm-arm-redefine-pmd_huge-with-pmd_leaf.patch
mm-arm64-merge-pxd_huge-and-pxd_leaf-definitions.patch
mm-powerpc-redefine-pxd_huge-with-pxd_leaf.patch
mm-gup-merge-pxd-huge-mapping-checks.patch
mm-treewide-replace-pxd_huge-with-pxd_leaf.patch
mm-treewide-remove-pxd_huge.patch
mm-arm-remove-pmd_thp_or_huge.patch
mm-document-pxd_leaf-api.patch
selftests-mm-run_vmtestssh-fix-hugetlb-mem-size-calculation.patch