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 X-Spam-Level: X-Spam-Status: No, score=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C24FC55179 for ; Fri, 6 Nov 2020 20:03:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0ABCA2072E for ; Fri, 6 Nov 2020 20:03:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=deltatee.com header.i=@deltatee.com header.b="dA51HxqS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728364AbgKFUDj (ORCPT ); Fri, 6 Nov 2020 15:03:39 -0500 Received: from ale.deltatee.com ([204.191.154.188]:60262 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727341AbgKFUDi (ORCPT ); Fri, 6 Nov 2020 15:03:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=deltatee.com; s=20200525; h=Subject:Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Sender: Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender :Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=eezeT8sE0c+dvLmjvESICoKhAlzXaqNnjl5jvhsWtf0=; b=dA51HxqSCHR4JuZbkzzSmg3W+t yWkoDic2Ka2INSPCZAs/OVNcm6A8oiWD4xs5cZOJI6JCJWoyIEcMFYQuwDXpEP94JRNOq4Jm597IW zY9+kL0WMddHMYyhT16mkNx04/hEioF70ZnVXsKAV6asL35LsLIGi/hQcp4flbFRG6VUJKaDSYlQm BxfqzK/sL5Uezm0Q9/fKyVYifXoPOzisxNKpvC7XUXwFcrIJEQsQ7vt00oqimgL0c3rksAR1njMyZ RHfHxAGvibWkE0XP5Ny8DbZ0h152CMHqRJ4Aq7wirLss+0t12x4iriBT6mcS0XfaFdtJXuwn2twYA onotgqBQ==; Received: from s01060023bee90a7d.cg.shawcable.net ([24.64.145.4] helo=[192.168.0.10]) by ale.deltatee.com with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1kb7xI-0005Wu-TX; Fri, 06 Nov 2020 13:03:30 -0700 To: Jason 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 , =?UTF-8?Q?Christian_K=c3=b6nig?= , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter References: <20201106170036.18713-1-logang@deltatee.com> <20201106170036.18713-15-logang@deltatee.com> <20201106172206.GS36674@ziepe.ca> <20201106174223.GU36674@ziepe.ca> <2c2d2815-165e-2ef9-60d6-3ace7ff3aaa5@deltatee.com> <20201106180922.GV36674@ziepe.ca> <09885400-36f8-bc1d-27f0-a8adcf6104d4@deltatee.com> <20201106193024.GW36674@ziepe.ca> <03032637-0826-da76-aec2-121902b1c166@deltatee.com> <20201106195341.GA244516@ziepe.ca> From: Logan Gunthorpe Message-ID: Date: Fri, 6 Nov 2020 13:03:26 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201106195341.GA244516@ziepe.ca> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 24.64.145.4 X-SA-Exim-Rcpt-To: daniel.vetter@ffwll.ch, willy@infradead.org, ddutile@redhat.com, jhubbard@nvidia.com, iweiny@intel.com, christian.koenig@amd.com, dan.j.williams@intel.com, hch@lst.de, sbates@raithlin.com, iommu@lists.linux-foundation.org, linux-mm@kvack.org, linux-pci@vger.kernel.org, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 14/15] PCI/P2PDMA: Introduce pci_mmap_p2pmem() X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-11-06 12:53 p.m., Jason Gunthorpe wrote: > On Fri, Nov 06, 2020 at 12:44:59PM -0700, Logan Gunthorpe wrote: >> >> >> On 2020-11-06 12:30 p.m., Jason Gunthorpe wrote: >>>> I certainly can't make decisions for code that isn't currently >>>> upstream. >>> >>> The rdma drivers are all upstream, what are you thinking about? >> >> Really? I feel like you should know what I mean here... >> >> I mean upstream code that actually uses the APIs that I'd have to >> introduce. I can't say here's an API feature that no code uses but the >> already upstream rdma driver might use eventually. It's fairly easy to >> send patches that make the necessary changes when someone adds a use of >> those changes inside the rdma code. > > Sure, but that doesn't mean you have to actively design things to be > unusable beyond this narrow case. The RDMA drivers are all there, all > upstream, if this work is accepted then the changes to insert P2P > pages into their existing mmap flows is a reasonable usecase to > consider at this point when building core code APIs. > > You shouldn't add dead code, but at least have a design in mind for > what it needs to look like and some allowance. I don't see anything I've done that's at odds with that. You will still need to make changes to the p2pdma code to implement your use case. >>>> Ultimately, if you aren't using the genpool you will have to implement >>>> your own mmap operation that somehow allocates the pages and your own >>>> page_free hook. >>> >>> Sure, the mlx5 driver already has a specialized alloctor for it's BAR >>> pages. >> >> So it *might* make sense to carve out a common helper to setup a VMA for >> P2PDMA to do the vm_flags check and set VM_MIXEDMAP... but besides that, >> there's no code that would be common to the two cases. > > I think the whole insertion of P2PDMA pages into a VMA should be > similar to io_remap_pfn() so all the VM flags, pgprot_decrypted and > other subtle details are all in one place. (also it needs a > pgprot_decrypted before doing vmf_insert, I just learned that this > month) I don't think a function like that will work for the p2pmem use case. In order to implement proper page freeing I expect I'll need a loop around the allocator and vm_insert_mixed()... Something roughly like: for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) { vaddr = pci_alloc_p2pmem(pdev, PAGE_SIZE); ret = vmf_insert_mixed(vma, addr, __pfn_to_pfn_t(virt_to_pfn(vaddr), PFN_DEV | PFN_MAP)); } That way we can call pci_free_p2pmem() when a page's ref count goes to zero. I suspect your use case will need to do something similar. Logan