+ mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm/userfaultfd: fix uffd-wp handling for THP migration entries
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: mm/userfaultfd: fix uffd-wp handling for THP migration entries
Date: Wed, 5 Apr 2023 18:02:35 +0200

Looks like what we fixed for hugetlb in commit 44f86392bdd1 ("mm/hugetlb:
fix uffd-wp handling for migration entries in
hugetlb_change_protection()") similarly applies to THP.

Setting/clearing uffd-wp on THP migration entries is not implemented
properly.  Further, while removing migration PMDs considers the uffd-wp
bit, inserting migration PMDs does not consider the uffd-wp bit.

We have to set/clear independently of the migration entry type in
change_huge_pmd() and properly copy the uffd-wp bit in
set_pmd_migration_entry().

Verified using a simple reproducer that triggers migration of a THP, that
the set_pmd_migration_entry() no longer loses the uffd-wp bit.

Link: https://lkml.kernel.org/r/20230405160236.587705-2-david@redhat.com
Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

--- a/mm/huge_memory.c~mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries
+++ a/mm/huge_memory.c
@@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *t
 	if (is_swap_pmd(*pmd)) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
 		struct page *page = pfn_swap_entry_to_page(entry);
+		pmd_t newpmd;
 
 		VM_BUG_ON(!is_pmd_migration_entry(*pmd));
 		if (is_writable_migration_entry(entry)) {
-			pmd_t newpmd;
 			/*
 			 * A protection check is difficult so
 			 * just be safe and disable write
@@ -1855,8 +1855,16 @@ int change_huge_pmd(struct mmu_gather *t
 				newpmd = pmd_swp_mksoft_dirty(newpmd);
 			if (pmd_swp_uffd_wp(*pmd))
 				newpmd = pmd_swp_mkuffd_wp(newpmd);
-			set_pmd_at(mm, addr, pmd, newpmd);
+		} else {
+			newpmd = *pmd;
 		}
+
+		if (uffd_wp)
+			newpmd = pmd_swp_mkuffd_wp(newpmd);
+		else if (uffd_wp_resolve)
+			newpmd = pmd_swp_clear_uffd_wp(newpmd);
+		if (!pmd_same(*pmd, newpmd))
+			set_pmd_at(mm, addr, pmd, newpmd);
 		goto unlock;
 	}
 #endif
@@ -3251,6 +3259,8 @@ int set_pmd_migration_entry(struct page_
 	pmdswp = swp_entry_to_pmd(entry);
 	if (pmd_soft_dirty(pmdval))
 		pmdswp = pmd_swp_mksoft_dirty(pmdswp);
+	if (pmd_uffd_wp(pmdval))
+		pmdswp = pmd_swp_mkuffd_wp(pmdswp);
 	set_pmd_at(mm, address, pvmw->pmd, pmdswp);
 	page_remove_rmap(page, vma, true);
 	put_page(page);
_

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

mm-userfaultfd-fix-uffd-wp-handling-for-thp-migration-entries.patch
m68k-mm-use-correct-bit-number-in-_page_swp_exclusive-comment.patch
mm-userfaultfd-dont-consider-uffd-wp-bit-of-writable-migration-entries.patch