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[79.242.57.10]) by smtp.gmail.com with ESMTPSA id a17sm13193206ejx.13.2021.04.20.08.17.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 20 Apr 2021 08:18:00 -0700 (PDT) Subject: Re: [PATCH v3 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: <20210420150049.14031-1-rppt@kernel.org> <20210420150049.14031-2-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat Message-ID: Date: Tue, 20 Apr 2021 17:17:58 +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: <20210420150049.14031-2-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 17:00, 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 | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index c3a17b189064..6515f82b0f32 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2080,13 +2080,15 @@ 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 (unlikely(page_is_secretmem(page))) { > + put_compound_head(head, 1, flags); > + goto pte_unmap; > + } > + > if (unlikely(pte_val(pte) != pte_val(*ptep))) { > put_compound_head(head, 1, flags); > goto pte_unmap; > Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb