linux-kernel - [PATCH v6 08/19] userfaultfd: wp: drop _PAGE_UFFD

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Message-Id: <20200220163112.11409-9-peterx@redhat.com>
Date:   Thu, 20 Feb 2020 11:31:01 -0500
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Brian Geffon <bgeffon@...gle.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        David Hildenbrand <david@...hat.com>, peterx@...hat.com,
        Martin Cracauer <cracauer@...s.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Bobby Powers <bobbypowers@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Maya Gokhale <gokhale2@...l.gov>,
        Johannes Weiner <hannes@...xchg.org>,
        Marty McFadden <mcfadden8@...l.gov>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Hugh Dickins <hughd@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Jerome Glisse <jglisse@...hat.com>
Subject: [PATCH v6 08/19] 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.

Reviewed-by: Jerome Glisse <jglisse@...hat.com>
Reviewed-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@...hat.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 c56a83e0a184..134bef68a1de 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1011,6 +1011,14 @@ 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 21cd818dfede..557837ec29c3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -785,6 +785,14 @@ 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);
-- 
2.24.1