+ mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.patch added to mm-hotfixes-unstable branch

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

The patch titled
     Subject: mm/hugetlb: fix uffd-wp handling for migration entries in hugetlb_change_protection()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.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/hugetlb: fix uffd-wp handling for migration entries in hugetlb_change_protection()
Date: Thu, 22 Dec 2022 21:55:11 +0100

We have to update the uffd-wp SWP PTE bit independent of the type of
migration entry.  Currently, if we're unlucky and we want to install/clear
the uffd-wp bit just while we're migrating a read-only mapped hugetlb
page, we would miss to set/clear the uffd-wp bit.

Further, if we're processing a readable-exclusive migration entry and
neither want to set or clear the uffd-wp bit, we could currently end up
losing the uffd-wp bit.  Note that the same would hold for writable
migrating entries, however, having a writable migration entry with the
uffd-wp bit set would already mean that something went wrong.

Note that the change from !is_readable_migration_entry ->
writable_migration_entry is harmless and actually cleaner, as raised by
Miaohe Lin and discussed in [1].

[1] https://lkml.kernel.org/r/90dd6a93-4500-e0de-2bf0-bf522c311b0c@huawei.com

Link: https://lkml.kernel.org/r/20221222205511.675832-3-david@redhat.com
Fixes: 60dfaad65aa9 ("mm/hugetlb: allow uffd wr-protect none ptes")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/hugetlb.c~mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection
+++ a/mm/hugetlb.c
@@ -6662,10 +6662,9 @@ unsigned long hugetlb_change_protection(
 		} else if (unlikely(is_hugetlb_entry_migration(pte))) {
 			swp_entry_t entry = pte_to_swp_entry(pte);
 			struct page *page = pfn_swap_entry_to_page(entry);
+			pte_t newpte = pte;
 
-			if (!is_readable_migration_entry(entry)) {
-				pte_t newpte;
-
+			if (is_writable_migration_entry(entry)) {
 				if (PageAnon(page))
 					entry = make_readable_exclusive_migration_entry(
 								swp_offset(entry));
@@ -6673,13 +6672,15 @@ unsigned long hugetlb_change_protection(
 					entry = make_readable_migration_entry(
 								swp_offset(entry));
 				newpte = swp_entry_to_pte(entry);
-				if (uffd_wp)
-					newpte = pte_swp_mkuffd_wp(newpte);
-				else if (uffd_wp_resolve)
-					newpte = pte_swp_clear_uffd_wp(newpte);
-				set_huge_pte_at(mm, address, ptep, newpte);
 				pages++;
 			}
+
+			if (uffd_wp)
+				newpte = pte_swp_mkuffd_wp(newpte);
+			else if (uffd_wp_resolve)
+				newpte = pte_swp_clear_uffd_wp(newpte);
+			if (!pte_same(pte, newpte))
+				set_huge_pte_at(mm, address, ptep, newpte);
 		} else if (unlikely(is_pte_marker(pte))) {
 			/* No other markers apply for now. */
 			WARN_ON_ONCE(!pte_marker_uffd_wp(pte));
_

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

mm-hugetlb-fix-pte-marker-handling-in-hugetlb_change_protection.patch
mm-hugetlb-fix-uffd-wp-handling-for-migration-entries-in-hugetlb_change_protection.patch