Date:   Sat, 18 Feb 2023 00:27:34 +0000
In-Reply-To: <20230218002819.1486479-1-jthoughton@google.com>
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References: <20230218002819.1486479-1-jthoughton@google.com>
Message-ID: <20230218002819.1486479-2-jthoughton@google.com>
Subject: [PATCH v2 01/46] 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>,
        Andrew Morton <akpm@linux-foundation.org>
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>,
        Frank van der Linden <fvdl@google.com>,
        Jiaqi Yan <jiaqiyan@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        James Houghton <jthoughton@google.com>
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Precedence: bulk

If would be bad if we actually set PageUptodate with UFFDIO_CONTINUE;
PageUptodate indicates that the page has been zeroed, and we don't want
to give 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>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 07abcb6eb203..792cb2e67ce5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6256,7 +6256,16 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	 * preceding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
-	__folio_mark_uptodate(folio);
+	if (!is_continue)
+		__folio_mark_uptodate(folio);
+	else if (!folio_test_uptodate(folio)) {
+		/*
+		 * This should never happen; HugeTLB pages are always Uptodate
+		 * as soon as they are allocated.
+		 */
+		ret = -EFAULT;
+		goto out_release_nounlock;
+	}
 
 	/* Add shared, newly allocated pages to the page cache. */
 	if (vm_shared && !is_continue) {
-- 
2.39.2.637.g21b0678d19-goog