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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id s2-20020a0cdc02000000b0065af9d1203dsm693210qvk.121.2023.11.23.10.02.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Nov 2023 10:02:23 -0800 (PST) From: Peter Xu To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: peterx@redhat.com, Andrew Morton , Dan Williams , Mel Gorman , Matthew Wilcox , "Aneesh Kumar K . V" , Christoph Hellwig Subject: [PATCH] mm/gup: Fix follow_devmap_p[mu]d() on page==NULL handling Date: Thu, 23 Nov 2023 13:02:22 -0500 Message-ID: <20231123180222.1048297-1-peterx@redhat.com> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" This is a bug found not by any report but only by code observations. When GUP sees a devpmd/devpud and if page=3D=3DNULL is returned, it means a fault is probably required. Here falling through when page=3D=3DNULL can c= ause unexpected behavior. Fix both cases by catching the page=3D=3DNULL cases with no_page_table(). Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings") Fixes: 080dbb618b4b ("mm/follow_page_mask: split follow_page_mask to smalle= r functions.") Cc: Dan Williams Cc: Mel Gorman Cc: Matthew Wilcox Cc: Aneesh Kumar K.V Cc: Christoph Hellwig Signed-off-by: Peter Xu Acked-by: David Hildenbrand --- mm/gup.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/gup.c b/mm/gup.c index 231711efa390..0a5f0e91bfec 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -710,6 +710,7 @@ static struct page *follow_pmd_mask(struct vm_area_stru= ct *vma, spin_unlock(ptl); if (page) return page; + return no_page_table(vma, flags); } if (likely(!pmd_trans_huge(pmdval))) return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); @@ -758,6 +759,7 @@ static struct page *follow_pud_mask(struct vm_area_stru= ct *vma, spin_unlock(ptl); if (page) return page; + return no_page_table(vma, flags); } if (unlikely(pud_bad(*pud))) return no_page_table(vma, flags); --=20 2.41.0