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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 A52E3C433E1 for ; Fri, 22 May 2020 14:04:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D05821534 for ; Fri, 22 May 2020 14:04:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729955AbgEVOEO (ORCPT ); Fri, 22 May 2020 10:04:14 -0400 Received: from foss.arm.com ([217.140.110.172]:36140 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729399AbgEVOEO (ORCPT ); Fri, 22 May 2020 10:04:14 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 94A22D6E; Fri, 22 May 2020 07:04:13 -0700 (PDT) Received: from e121166-lin.cambridge.arm.com (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9F8B13F68F; Fri, 22 May 2020 07:04:10 -0700 (PDT) Date: Fri, 22 May 2020 15:04:07 +0100 From: Lorenzo Pieralisi To: Alan Mikhak Cc: gustavo.pimentel@synopsys.com, alan.mikhak@sifive.com, amurray@thegoodpenguin.co.uk, bhelgaas@google.com, helgaas@kernel.org, jingoohan1@gmail.com, jonathanh@nvidia.com, kthota@nvidia.com, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, mmaddireddy@nvidia.com, sagar.tv@gmail.com, thierry.reding@gmail.com, vidyas@nvidia.com, Alan Mikhak Subject: Re: PCI: dwc: Warn only for non-prefetchable memory resource size >4GB Message-ID: <20200522140406.GH11785@e121166-lin.cambridge.arm.com> References: <20200520023304.14348-1-amikhak@wirelessfabric.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200520023304.14348-1-amikhak@wirelessfabric.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 19, 2020 at 07:33:04PM -0700, Alan Mikhak wrote: > Hi Lorenzo, > > I came across this issue when implementing a Linux NVMe endpoint function > driver under the Linux PCI Endpoint Framework: > https://lwn.net/Articles/804369/ > > I needed to map up to 128GB of host memory using a single ATU window > from the endpoint side because NVMe PRPs can be scattered all over host > memory. In the process, I came across this 4GB limitation where the > maximum size of memory that can be mapped is limited by what a u32 value > can represent. > > I submitted a separate patch to fix an undefined behavior that may also > happen in dw_pcie_prog_outbound_atu_unroll() under some circumstances > when the size of the memory being mapped is greater than what a u32 value > can represent. > https://patchwork.kernel.org/patch/11469701/ > > The above patch has been accepted. However, the variable pp->mem_size > in dw_pcie_host_init() is still a u32 whereas the value returned by > resource_size() is u64. If the resource size has non-zero upper 32-bits, > those upper 32-bits will be lost when assigning: > pp->mem_size = resource_size(pp->mem). > > Since current callers seem happy with the existing 4GB implementation > and fixing the u32 limit is beyond my available resources and has a long > high-impact tail, a warning seemed to be a good choice to highlight > this issue in case someone else decides to map a MEM region that is > greater than 4GB. > > Removing the warning will avoid such discussions. Without this warning, > this limitation will go unnoticed and will only impact whoever has to > deal with it. It cost me time to figure it out when I had an application > that needed a region larger than 4GB. I figured the most I could do about > it is to raise the issue by adding a warning. You did the right thing (and you helped me unearth some major deficiencies in current DWC code). Unfortunately I have to drop: 9e73fa02aa00 ("PCI: dwc: Warn if MEM resource size exceeds max for 32-bits") because it triggers regressions (and it is still not in the mainline, IMO there would be more if we send it upstream). I will keep: e1fc129219a8 ("PCI: dwc: Program outbound ATU upper limit register") because it is a step in the right direction and makes sense on its own. Thanks for all the effort you put into this. Lorenzo > Regards, > Alan > > > > > >