+ mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch added to -mm tree

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

The patch titled
     Subject: mm/shmem: allows file-back mem to be uffd wr-protected on thps
has been added to the -mm tree.  Its filename is
     mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps.patch

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------------------------------------------------------
From: Peter Xu <peterx@redhat.com>
Subject: mm/shmem: allows file-back mem to be uffd wr-protected on thps

We don't have "huge" version of pte markers, instead when necessary we
split the thp.

However split the thp is not enough, because file-backed thp is handled
totally differently comparing to anonymous thps: rather than doing a real
split, the thp pmd will simply got cleared in __split_huge_pmd_locked().

That is not enough if e.g.  when there is a thp covers range [0, 2M) but
we want to wr-protect small page resides in [4K, 8K) range, because after
__split_huge_pmd() returns, there will be a none pmd, and
change_pmd_range() will just skip it right after the split.

Here we leverage the previously introduced change_pmd_prepare() macro so
that we'll populate the pmd with a pgtable page after the pmd split (in
which process the pmd will be cleared for cases like shmem).  Then
change_pte_range() will do all the rest for us by installing the uffd-wp
pte marker at any none pte that we'd like to wr-protect.

Link: https://lkml.kernel.org/r/20220405014852.14413-1-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>
---

 mm/mprotect.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/mprotect.c~mm-shmem-allows-file-back-mem-to-be-uffd-wr-protected-on-thps
+++ a/mm/mprotect.c
@@ -338,8 +338,15 @@ static inline unsigned long change_pmd_r
 		}
 
 		if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
-			if (next - addr != HPAGE_PMD_SIZE) {
+			if ((next - addr != HPAGE_PMD_SIZE) ||
+			    uffd_wp_protect_file(vma, cp_flags)) {
 				__split_huge_pmd(vma, pmd, addr, false, NULL);
+				/*
+				 * For file-backed, the pmd could have been
+				 * cleared; make sure pmd populated if
+				 * necessary, then fall-through to pte level.
+				 */
+				change_pmd_prepare(vma, pmd, cp_flags);
 			} else {
 				/*
 				 * change_huge_pmd() does not defer TLB flushes,
_

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