FAILED: patch "[PATCH] mm/userfaultfd: fix uffd-wp handling for THP migration" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 24bf08c4376be417f16ceb609188b16f461b0443
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023042216-retainer-immersion-5428@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

24bf08c4376b ("mm/userfaultfd: fix uffd-wp handling for THP migration entries") 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive") 6c54dc6c7437 ("mm/rmap: use page_move_anon_rmap() when reusing a mapped PageAnon() page exclusively") 28c5209dfd5f ("mm/rmap: pass rmap flags to hugepage_add_anon_rmap()")
f1e2db12e45b ("mm/rmap: remove do_page_add_anon_rmap()")
14f9135d5470 ("mm/rmap: convert RMAP flags to a proper distinct rmap_t type") fb3d824d1a46 ("mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()") b51ad4f8679e ("mm/memory: slightly simplify copy_present_pte()")
623a1ddfeb23 ("mm/hugetlb: take src_mm->write_protect_seq in copy_hugetlb_page_range()") 3bff7e3f1f16 ("mm/huge_memory: streamline COW logic in do_huge_pmd_wp_page()") c145e0b47c77 ("mm: streamline COW logic in do_swap_page()")
84d60fdd3733 ("mm: slightly clarify KSM logic in do_swap_page()")
53a05ad9f21d ("mm: optimize do_wp_page() for exclusive pages in the swapcache") 9030fb0bb9d6 ("Merge tag 'folio-5.18c' of git://git.infradead.org/users/willy/pagecache")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 24bf08c4376be417f16ceb609188b16f461b0443 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <[email protected]>
Date: Wed, 5 Apr 2023 18:02:35 +0200
Subject: [PATCH] mm/userfaultfd: fix uffd-wp handling for THP migration
entries

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.

index 032fb0ef9cd1..e3706a2b34b2 100644
@@ -1838,10 +1838,10 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	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 *tlb, struct vm_area_struct *vma,
 				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_vma_mapped_walk *pvmw,
 	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);