[PATCH v6 08/19] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork

From: Peter Xu <peterx@redhat.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Brian Geffon <bgeffon@google.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	David Hildenbrand <david@redhat.com>,
	peterx@redhat.com, Martin Cracauer <cracauer@cons.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Mel Gorman <mgorman@suse.de>,
	Bobby Powers <bobbypowers@gmail.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Maya Gokhale <gokhale2@llnl.gov>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Marty McFadden <mcfadden8@llnl.gov>,
	Denis Plotnikov <dplotnikov@virtuozzo.com>,
	Hugh Dickins <hughd@google.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	Jerome Glisse <jglisse@redhat.com>
Subject: [PATCH v6 08/19] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork
Date: Thu, 20 Feb 2020 11:31:01 -0500	[thread overview]
Message-ID: <20200220163112.11409-9-peterx@redhat.com> (raw)
In-Reply-To: <20200220163112.11409-1-peterx@redhat.com>

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@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@redhat.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

