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Tue, 05 Jul 2022 12:16:49 -0600 Message-ID: Date: Tue, 5 Jul 2022 12:16:45 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Content-Language: en-CA To: Greg Kroah-Hartman Cc: Christoph Hellwig , Jason Gunthorpe , 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 , Dan Williams , =?UTF-8?Q?Christian_K=c3=b6nig?= , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin , Bjorn Helgaas , Ira Weiny , Robin Murphy , Martin Oliveira , Chaitanya Kulkarni , Ralph Campbell , Bjorn Helgaas References: <20220629175906.GU23621@ziepe.ca> <20220705075108.GB17451@lst.de> <20220705135102.GE23621@ziepe.ca> <20220705161240.GB13721@lst.de> <20220705164315.GB14484@lst.de> <20220705165039.GB14566@lst.de> <1bd43ef7-0403-bd25-087c-d54d5af677e4@deltatee.com> From: Logan Gunthorpe In-Reply-To: Content-Type: text/plain; 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dkim=pass header.d=deltatee.com header.s=20200525 header.b="lfZ2jUE/"; spf=pass (imf24.hostedemail.com: domain of logang@deltatee.com designates 204.191.154.188 as permitted sender) smtp.mailfrom=logang@deltatee.com; dmarc=pass (policy=none) header.from=deltatee.com X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1657045017-88209 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 2022-07-05 11:42, Greg Kroah-Hartman wrote: > On Tue, Jul 05, 2022 at 11:32:23AM -0600, Logan Gunthorpe wrote: >> >> >> On 2022-07-05 11:21, Greg Kroah-Hartman wrote: >>> On Tue, Jul 05, 2022 at 06:50:39PM +0200, Christoph Hellwig wrote: >>>> [note for the newcomers, this is about allowing mmap()ing the PCIe >>>> P2P memory from the generic PCI P2P code through sysfs, and more >>>> importantly how to revoke it on device removal] >>> >>> We allow mmap on PCIe config space today, right? Why is this different >>> from what pci_create_legacy_files() does today? >>> >>>> On Tue, Jul 05, 2022 at 10:44:49AM -0600, Logan Gunthorpe wrote: >>>>> We might be able to. I'm not sure. I'll have to figure out how to find >>>>> that inode from the p2pdma code. I haven't found an obvious interface to >>>>> do that. >>>> >>>> I think the right way to approach this would be a new sysfs API >>>> that internally calls unmap_mapping_range internally instead of >>>> exposing the inode. I suspect that might actually be the right thing >>>> to do for iomem_inode as well. >>> >>> Why do we need something new and how is this any different from the PCI >>> binary files I mention above? We have supported PCI hotplug for a very >>> long time, do the current PCI binary sysfs files not work properly with >>> mmap and removing a device? >> >> The P2PDMA code allocates and hands out struct pages to userspace that >> are backed with ZONE_DEVICE memory from a device's BAR. This is quite >> different from the existing binary files mentioned above which neither >> support struct pages nor allocation. > > Why would you want to do this through a sysfs interface? that feels > horrid... The current version does it through a char device, but that requires creating a simple_fs and anon_inode for teardown on driver removal, plus a bunch of hooks through the driver that exposes it (NVMe, in this case) to set this all up. Christoph is suggesting a sysfs interface which could potentially avoid the anon_inode and all of the extra hooks. It has some significant benefits and maybe some small downsides, but I wouldn't describe it as horrid. Logan