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Tue, 28 Sep 2021 12:47:08 -0700 (PDT) Received: from ziepe.ca ([206.223.160.26]) by smtp.gmail.com with ESMTPSA id d14sm79297qkg.49.2021.09.28.12.47.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Sep 2021 12:47:08 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mVJ4F-007GbK-31; Tue, 28 Sep 2021 16:47:07 -0300 Date: Tue, 28 Sep 2021 16:47:07 -0300 From: Jason Gunthorpe To: Logan Gunthorpe Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Stephen Bates , Christoph Hellwig , Dan Williams , Christian =?utf-8?B?S8O2bmln?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy , Martin Oliveira , Chaitanya Kulkarni Subject: Re: [PATCH v3 14/20] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages Message-ID: <20210928194707.GU3544071@ziepe.ca> References: <20210916234100.122368-1-logang@deltatee.com> <20210916234100.122368-15-logang@deltatee.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210916234100.122368-15-logang@deltatee.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 2256E6001989 X-Stat-Signature: iykn3nzig3ptax5om4kt6uh37sota4he Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=EO1kDwze; dmarc=none; spf=pass (imf10.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.222.182 as permitted sender) smtp.mailfrom=jgg@ziepe.ca X-HE-Tag: 1632858428-559434 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 Thu, Sep 16, 2021 at 05:40:54PM -0600, Logan Gunthorpe wrote: > Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to > allow obtaining P2PDMA pages. If a caller does not set this flag > and tries to map P2PDMA pages it will fail. > > This is implemented by adding a flag and a check to get_dev_pagemap(). I would like to see the get_dev_pagemap() deleted from GUP in the first place. Why isn't this just a simple check of the page->pgmap type after acquiring a valid page reference? See my prior note Jason