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=-2.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 AE2F4C10F0E for ; Thu, 18 Apr 2019 17:24:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 72D8D206B6 for ; Thu, 18 Apr 2019 17:24:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555608268; bh=98mzb1UFPSp9bcl6Oy6xtKDs4Kg4g5u/BA/rkRnkjcU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=12zyN5pW43Mu3IOetkCJd6NOmhwHmS0ANFhKKN/S3aowdP6yZWcs26EeNTgdxqht1 17+Mgb6YT9maxxqBxbOmSFbNtR2VYSrzteXRc8UohZjdoqum3bW2gJ6fRuMqc7+N8N iZCWQlNOmWlZnnLpAp4bqwukG4myJw5v5XNyv5Xg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388346AbfDRRY1 (ORCPT ); Thu, 18 Apr 2019 13:24:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:39880 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733067AbfDRRY1 (ORCPT ); Thu, 18 Apr 2019 13:24:27 -0400 Received: from localhost (odyssey.drury.edu [64.22.249.253]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 05A2E20693; Thu, 18 Apr 2019 17:24:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555608267; bh=98mzb1UFPSp9bcl6Oy6xtKDs4Kg4g5u/BA/rkRnkjcU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XdEWaFZnhagtnCnbhdmwLzVrrQoIgxc+QA2/H7EaPCDLTrfDDbsGj4NB2jpV2digw zvUav0PdSLj85Mi40dpFRLLrv0DLkrS3kRDAYvawWSYo//y4Rixo7pae2FzMH6Z7YF AIFedt02s3NAXLGL40TFic4jRjvTHaFuhd3dTHTk= Date: Thu, 18 Apr 2019 12:24:26 -0500 From: Bjorn Helgaas To: Logan Gunthorpe Cc: Christian =?iso-8859-1?Q?K=F6nig?= , rdunlap@infradead.org, linux-pci@vger.kernel.org Subject: Re: [PATCH] PCI/P2PDMA: start with a whitelist for root complexes Message-ID: <20190418172426.GB213349@google.com> References: <20190418115859.2394-1-christian.koenig@amd.com> <20190418163347.GA213349@google.com> <22b686f0-572b-d083-915f-5c46c89dfbc3@deltatee.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <22b686f0-572b-d083-915f-5c46c89dfbc3@deltatee.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, Apr 18, 2019 at 10:58:55AM -0600, Logan Gunthorpe wrote: > On 2019-04-18 10:33 a.m., Bjorn Helgaas wrote: > > On Thu, Apr 18, 2019 at 01:58:59PM +0200, Christian König wrote: > > > A lot of root complexes can still do P2P even when PCI devices > > > don't share a common upstream bridge. > > > > > > Start adding a whitelist and allow P2P if both participants are > > > attached to known good root complex. > > > > Is there a plan for addressing this in a generic way that doesn't > > require an OS modification for every new "known good root complex", > > e.g., some PCIe or ACPI spec update that allows the OS to discover > > this? > > I'm aware of work going on in the PCI SIG to address this [1]. > > But I expect it's going to be a long time before actual hardware advertises > this capability to indicate support. So in the interim we either need to not > use p2pdma on root complexes or create a white list. I'm in favour of the > white list approach. I agree we need a whitelist; I just want to make sure we also make progress on some way to limit the amount of time we need to update it. > [1] https://lore.kernel.org/linux-pci/20181210115653.0000615a@huawei.com/