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Date:   Fri, 21 Oct 2022 16:36:17 +0000
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Subject: [RFC PATCH v2 01/47] hugetlb: don't set PageUptodate for UFFDIO_CONTINUE
From:   James Houghton <jthoughton@google.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        James Houghton <jthoughton@google.com>
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Precedence: bulk

This is how it should have been to begin with. It would be very bad if
we actually set PageUptodate with a UFFDIO_CONTINUE, as UFFDIO_CONTINUE
doesn't actually set/update the contents of the page, so we would be
exposing a non-zeroed page to the user.

The reason this change is being made now is because UFFDIO_CONTINUEs on
subpages definitely shouldn't set this page flag on the head page.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1a7dc7b2e16c..650761cdd2f6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6097,7 +6097,10 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	 * preceding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
-	__SetPageUptodate(page);
+	if (!is_continue)
+		__SetPageUptodate(page);
+	else
+		VM_WARN_ON_ONCE_PAGE(!PageUptodate(page), page);
 
 	/* Add shared, newly allocated pages to the page cache. */
 	if (vm_shared && !is_continue) {
-- 
2.38.0.135.g90850a2211-goog