From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C611CCCA47B for ; Tue, 5 Jul 2022 18:16:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232690AbiGESQ5 (ORCPT ); Tue, 5 Jul 2022 14:16:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231372AbiGESQy (ORCPT ); Tue, 5 Jul 2022 14:16:54 -0400 Received: from ale.deltatee.com (ale.deltatee.com [204.191.154.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E194B13F16; Tue, 5 Jul 2022 11:16:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=deltatee.com; s=20200525; h=Subject:In-Reply-To:From:References:Cc:To: MIME-Version:Date:Message-ID:content-disposition; bh=3rV+tiVBCGETS+0m1VAyBeVrP084h9ybGuEcnOkL1jA=; b=lfZ2jUE/Pcr0euHS/PfSv8pLp+ 4/PPUzTkxnoApUidHmt7v626OqXgmL9EfNAu2FXDE82dIkZS4evTLlHJEcLA0sTsaZOdUL7sJXe1K llHNHqCgIXLxKGdC2EFMJ+uJ5Hokog7lmJrw7QTYdr9sTAhi3Hh9CcwjoJd4Ouhncx4sMJASxJZo5 Z45htSKhX9sgtg0ghREzgU5ID+skNQqwC9IlBlCgbwMhIXpFTCZpyt8HpOowWyAcZWE8tHzKxRvGy MFCCqqfCCaFi3VeOomss+vTbx17EVsq2HRcn8flYVkfHi6Hg6MM5xYspG5eOMY/FjnLQKBs2TXntf tmVTSv/w==; Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1o8n6O-007Udo-RE; 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; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: gregkh@linuxfoundation.org, hch@lst.de, jgg@ziepe.ca, 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, sbates@raithlin.com, dan.j.williams@intel.com, christian.koenig@amd.com, jhubbard@nvidia.com, ddutile@redhat.com, willy@infradead.org, daniel.vetter@ffwll.ch, dave.b.minturn@intel.com, jason@jlekstrand.net, dave.hansen@linux.intel.com, jianxin.xiong@intel.com, helgaas@kernel.org, ira.weiny@intel.com, robin.murphy@arm.com, martin.oliveira@eideticom.com, ckulkarnilinux@gmail.com, rcampbell@nvidia.com, bhelgaas@google.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v7 20/21] PCI/P2PDMA: Introduce pci_mmap_p2pmem() X-SA-Exim-Version: 4.2.1 (built Sat, 13 Feb 2021 17:57:42 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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