[Devel] [PATCH RHEL8 COMMIT] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.6
------>
commit 1eb67309f9b8ff54644dec7e3cf966a7f97282df
Author: Peter Xu <peterx at redhat.com>
Date:   Mon Apr 20 10:34:39 2020 +0300

    userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork
    
    UFFD_EVENT_FORK support for uffd-wp should be already there, except that
    we should clean the uffd-wp bit if uffd fork event is not enabled.  Detect
    that to avoid _PAGE_UFFD_WP being set even if the VMA is not being tracked
    by VM_UFFD_WP.  Do this for both small PTEs and huge PMDs.
    
    Signed-off-by: Peter Xu <peterx at redhat.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Reviewed-by: Jerome Glisse <jglisse at redhat.com>
    Reviewed-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
    Cc: Andrea Arcangeli <aarcange at redhat.com>
    Cc: Bobby Powers <bobbypowers at gmail.com>
    Cc: Brian Geffon <bgeffon at google.com>
    Cc: David Hildenbrand <david at redhat.com>
    Cc: Denis Plotnikov <dplotnikov at virtuozzo.com>
    Cc: "Dr . David Alan Gilbert" <dgilbert at redhat.com>
    Cc: Hugh Dickins <hughd at google.com>
    Cc: Johannes Weiner <hannes at cmpxchg.org>
    Cc: "Kirill A . Shutemov" <kirill at shutemov.name>
    Cc: Martin Cracauer <cracauer at cons.org>
    Cc: Marty McFadden <mcfadden8 at llnl.gov>
    Cc: Maya Gokhale <gokhale2 at llnl.gov>
    Cc: Mel Gorman <mgorman at suse.de>
    Cc: Mike Kravetz <mike.kravetz at oracle.com>
    Cc: Pavel Emelyanov <xemul at openvz.org>
    Cc: Rik van Riel <riel at redhat.com>
    Cc: Shaohua Li <shli at fb.com>
    Link: http://lkml.kernel.org/r/20200220163112.11409-9-peterx@redhat.com
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-102938
    (cherry picked from commit b569a1760782f3da03ff718d61f74163dea599ff)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/huge_memory.c | 8 ++++++++
 mm/memory.c      | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index be580b411a6a..b26c2daf3547 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -921,6 +921,14 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	ret = -EAGAIN;
 	pmd = *src_pmd;
 
+	/*
+	 * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
+	 * does not have the VM_UFFD_WP, which means that the uffd
+	 * fork event is not enabled.
+	 */
+	if (!(vma->vm_flags & VM_UFFD_WP))
+		pmd = pmd_clear_uffd_wp(pmd);
+
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 	if (unlikely(is_swap_pmd(pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(pmd);
diff --git a/mm/memory.c b/mm/memory.c
index dc267ae5b293..7e0189d729e3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1037,6 +1037,14 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		pte = pte_mkclean(pte);
 	pte = pte_mkold(pte);
 
+	/*
+	 * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
+	 * does not have the VM_UFFD_WP, which means that the uffd
+	 * fork event is not enabled.
+	 */
+	if (!(vm_flags & VM_UFFD_WP))
+		pte = pte_clear_uffd_wp(pte);
+
 	page = vm_normal_page(vma, addr, pte);
 	if (page) {
 		get_page(page);