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[142.68.57.212]) by smtp.gmail.com with ESMTPSA id s49sm4525733qtc.29.2020.03.18.05.15.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 18 Mar 2020 05:15:04 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1jEXbC-0003dR-W7; Wed, 18 Mar 2020 09:15:03 -0300 Date: Wed, 18 Mar 2020 09:15:02 -0300 From: Jason Gunthorpe To: Pingfan Liu Cc: linux-mm@kvack.org, Ira Weiny , Andrew Morton , Mike Rapoport , Dan Williams , Matthew Wilcox , John Hubbard , "Aneesh Kumar K.V" , Christoph Hellwig , Shuah Khan , linux-kernel@vger.kernel.org Subject: Re: [PATCHv7 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path Message-ID: <20200318121502.GA13926@ziepe.ca> References: <1584333244-10480-3-git-send-email-kernelfans@gmail.com> <1584445652-30064-1-git-send-email-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1584445652-30064-1-git-send-email-kernelfans@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 17, 2020 at 07:47:32PM +0800, Pingfan Liu wrote: > FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is > going to be given to hardware and can't move. It would truncate CMA > permanently and should be excluded. > > In gup slow path, slow path, where > __gup_longterm_locked->check_and_migrate_cma_pages() handles FOLL_LONGTERM, > but in fast path, there lacks such a check, which means a possible leak of > CMA page to longterm pinned. > > Place a check in try_grab_compound_head() in the fast path to fix the leak, > and if FOLL_LONGTERM happens on CMA, it will fall back to slow path to > migrate the page. > > Some note about the check: > Huge page's subpages have the same migrate type due to either > allocation from a free_list[] or alloc_contig_range() with param > MIGRATE_MOVABLE. So it is enough to check on a single subpage > by is_migrate_cma_page(subpage) > > Signed-off-by: Pingfan Liu > Cc: Ira Weiny > Cc: Andrew Morton > Cc: Mike Rapoport > Cc: Dan Williams > Cc: Matthew Wilcox > Cc: John Hubbard > Cc: "Aneesh Kumar K.V" > Cc: Christoph Hellwig > Cc: Shuah Khan > Cc: Jason Gunthorpe > To: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > v6 -> v7: fix coding style issue > mm/gup.c | 9 +++++++++ > 1 file changed, 9 insertions(+) Much clearer, thank you Reviewed-by: Jason Gunthorpe Jason