+ mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch added to -mm tree

+ mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: mm/hugetlb: take care of UFFDIO_COPY_MODE_WP
has been added to the -mm tree.  Its filename is
     mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch

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------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm/hugetlb: take care of UFFDIO_COPY_MODE_WP

Pass the wp_copy variable into hugetlb_mcopy_atomic_pte() thoughout the
stack.  Apply the UFFD_WP bit if UFFDIO_COPY_MODE_WP is with UFFDIO_COPY.

Hugetlb pages are only managed by hugetlbfs, so we're safe even without
setting dirty bit in the huge pte if the page is installed as read-only. 
However we'd better still keep the dirty bit set for a read-only
UFFDIO_COPY pte (when UFFDIO_COPY_MODE_WP bit is set), not only to match
what we do with shmem, but also because the page does contain dirty data
that the kernel just copied from the userspace.

Link: https://lkml.kernel.org/r/20220405014904.14643-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/hugetlb.h |    6 ++++--
 mm/hugetlb.c            |   29 +++++++++++++++++++++++------
 mm/userfaultfd.c        |   14 +++++++++-----
 3 files changed, 36 insertions(+), 13 deletions(-)

--- a/include/linux/hugetlb.h~mm-hugetlb-take-care-of-uffdio_copy_mode_wp
+++ a/include/linux/hugetlb.h
@@ -160,7 +160,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 				unsigned long dst_addr,
 				unsigned long src_addr,
 				enum mcopy_atomic_mode mode,
-				struct page **pagep);
+				struct page **pagep,
+				bool wp_copy);
 #endif /* CONFIG_USERFAULTFD */
 bool hugetlb_reserve_pages(struct inode *inode, long from, long to,
 						struct vm_area_struct *vma,
@@ -356,7 +357,8 @@ static inline int hugetlb_mcopy_atomic_p
 						unsigned long dst_addr,
 						unsigned long src_addr,
 						enum mcopy_atomic_mode mode,
-						struct page **pagep)
+						struct page **pagep,
+						bool wp_copy)
 {
 	BUG();
 	return 0;
--- a/mm/hugetlb.c~mm-hugetlb-take-care-of-uffdio_copy_mode_wp
+++ a/mm/hugetlb.c
@@ -5795,7 +5795,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 			    unsigned long dst_addr,
 			    unsigned long src_addr,
 			    enum mcopy_atomic_mode mode,
-			    struct page **pagep)
+			    struct page **pagep,
+			    bool wp_copy)
 {
 	bool is_continue = (mode == MCOPY_ATOMIC_CONTINUE);
 	struct hstate *h = hstate_vma(dst_vma);
@@ -5925,7 +5926,12 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		goto out_release_unlock;
 
 	ret = -EEXIST;
-	if (!huge_pte_none(huge_ptep_get(dst_pte)))
+	/*
+	 * We allow to overwrite a pte marker: consider when both MISSING|WP
+	 * registered, we firstly wr-protect a none pte which has no page cache
+	 * page backing it, then access the page.
+	 */
+	if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
 		goto out_release_unlock;
 
 	if (vm_shared) {
@@ -5935,17 +5941,28 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		hugepage_add_new_anon_rmap(page, dst_vma, dst_addr);
 	}
 
-	/* For CONTINUE on a non-shared VMA, don't set VM_WRITE for CoW. */
-	if (is_continue && !vm_shared)
+	/*
+	 * For either: (1) CONTINUE on a non-shared VMA, or (2) UFFDIO_COPY
+	 * with wp flag set, don't set pte write bit.
+	 */
+	if (wp_copy || (is_continue && !vm_shared))
 		writable = 0;
 	else
 		writable = dst_vma->vm_flags & VM_WRITE;
 
 	_dst_pte = make_huge_pte(dst_vma, page, writable);
-	if (writable)
-		_dst_pte = huge_pte_mkdirty(_dst_pte);
+	/*
+	 * Always mark UFFDIO_COPY page dirty; note that this may not be
+	 * extremely important for hugetlbfs for now since swapping is not
+	 * supported, but we should still be clear in that this page cannot be
+	 * thrown away at will, even if write bit not set.
+	 */
+	_dst_pte = huge_pte_mkdirty(_dst_pte);
 	_dst_pte = pte_mkyoung(_dst_pte);
 
+	if (wp_copy)
+		_dst_pte = huge_pte_mkuffd_wp(_dst_pte);
+
 	set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 
 	(void)huge_ptep_set_access_flags(dst_vma, dst_addr, dst_pte, _dst_pte,
--- a/mm/userfaultfd.c~mm-hugetlb-take-care-of-uffdio_copy_mode_wp
+++ a/mm/userfaultfd.c
@@ -305,7 +305,8 @@ static __always_inline ssize_t __mcopy_a
 					      unsigned long dst_start,
 					      unsigned long src_start,
 					      unsigned long len,
-					      enum mcopy_atomic_mode mode)
+					      enum mcopy_atomic_mode mode,
+					      bool wp_copy)
 {
 	int vm_shared = dst_vma->vm_flags & VM_SHARED;
 	ssize_t err;
@@ -393,7 +394,7 @@ retry:
 		}
 
 		if (mode != MCOPY_ATOMIC_CONTINUE &&
-		    !huge_pte_none(huge_ptep_get(dst_pte))) {
+		    !huge_pte_none_mostly(huge_ptep_get(dst_pte))) {
 			err = -EEXIST;
 			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 			i_mmap_unlock_read(mapping);
@@ -401,7 +402,8 @@ retry:
 		}
 
 		err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
-					       dst_addr, src_addr, mode, &page);
+					       dst_addr, src_addr, mode, &page,
+					       wp_copy);
 
 		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 		i_mmap_unlock_read(mapping);
@@ -456,7 +458,8 @@ extern ssize_t __mcopy_atomic_hugetlb(st
 				      unsigned long dst_start,
 				      unsigned long src_start,
 				      unsigned long len,
-				      enum mcopy_atomic_mode mode);
+				      enum mcopy_atomic_mode mode,
+				      bool wp_copy);
 #endif /* CONFIG_HUGETLB_PAGE */
 
 static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
@@ -576,7 +579,8 @@ retry:
 	 */
 	if (is_vm_hugetlb_page(dst_vma))
 		return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
-						src_start, len, mcopy_mode);
+					       src_start, len, mcopy_mode,
+					       wp_copy);
 
 	if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 		goto out_unlock;
_

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

mm-introduce-pte_marker-swap-entry.patch
mm-teach-core-mm-about-pte-markers.patch
mm-check-against-orig_pte-for-finish_fault.patch
mm-uffd-pte_marker_uffd_wp.patch
mm-shmem-take-care-of-uffdio_copy_mode_wp.patch
mm-shmem-handle-uffd-wp-special-pte-in-page-fault-handler.patch
mm-shmem-persist-uffd-wp-bit-across-zapping-for-file-backed.patch
mm-shmem-allow-uffd-wr-protect-none-pte-for-file-backed-mem.patch
mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch
mm-shmem-handle-uffd-wp-during-fork.patch
mm-hugetlb-introduce-huge-pte-version-of-uffd-wp-helpers.patch
mm-hugetlb-hook-page-faults-for-uffd-write-protection.patch
mm-hugetlb-take-care-of-uffdio_copy_mode_wp.patch
mm-hugetlb-handle-uffdio_writeprotect.patch
mm-hugetlb-handle-pte-markers-in-page-faults.patch
mm-hugetlb-allow-uffd-wr-protect-none-ptes.patch
mm-hugetlb-only-drop-uffd-wp-special-pte-if-required.patch
mm-hugetlb-handle-uffd-wp-during-fork.patch
mm-khugepaged-dont-recycle-vma-pgtable-if-uffd-wp-registered.patch
mm-pagemap-recognize-uffd-wp-bit-for-shmem-hugetlbfs.patch
mm-uffd-enable-write-protection-for-shmem-hugetlbfs.patch
mm-enable-pte-markers-by-default.patch
selftests-uffd-enable-uffd-wp-for-shmem-hugetlbfs.patch