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[79.242.57.10]) by smtp.gmail.com with ESMTPSA id f6sm3291518wmf.28.2021.04.20.06.19.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Apr 2021 06:19:58 -0700 (PDT) Subject: Re: [PATCH v2 1/2] secretmem/gup: don't check if page is secretmem without reference To: Mike Rapoport , Andrew Morton Cc: Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Matthew Garrett , Mark Rutland , Michal Hocko , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , "Rafael J. Wysocki" , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , Yury Norov , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org References: <20210420131611.8259-1-rppt@kernel.org> <20210420131611.8259-2-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat Message-ID: <95b7fa81-f72e-c63f-0456-4c25dee8a5eb@redhat.com> Date: Tue, 20 Apr 2021 15:19:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210420131611.8259-2-rppt@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20.04.21 15:16, Mike Rapoport wrote: > From: Mike Rapoport > > The check in gup_pte_range() whether a page belongs to a secretmem mapping > is performed before grabbing the page reference. > > To avoid potential race move the check after try_grab_compound_head(). > > Signed-off-by: Mike Rapoport > --- > mm/gup.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index c3a17b189064..4b58c016e949 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > VM_BUG_ON(!pfn_valid(pte_pfn(pte))); > page = pte_page(pte); > > - if (page_is_secretmem(page)) > - goto pte_unmap; > - > head = try_grab_compound_head(page, 1, flags); > if (!head) > goto pte_unmap; > > + if (page_is_secretmem(page)) > + goto pte_unmap; > + Looking at the hunk below, I wonder if you're missing a put_compound_head(). (also, I'd do if unlikely(page_is_secretmem()) but that's a different discussion) > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > put_compound_head(head, 1, flags); > goto pte_unmap; > -- Thanks, David / dhildenb