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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FAKE_REPLY_C,MAILING_LIST_MULTI,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 ED502C2BA83 for ; Wed, 12 Feb 2020 14:16:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF4E120873 for ; Wed, 12 Feb 2020 14:16:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581517011; bh=EDVlPbawIuilZtpfWWUkGXCCUrkEzGW0hagfusO+Ufg=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=cjUkx9msTvtUPhbBRiOK2F7yam3Z1hvx5geqNrk2aQBrTjsFOao63x0K6bdWOrHKz XiQ1OW2GiMIcvPmgqREYyEtHmI4340He93A2zJjJjEnWCMwI8c4G2DAWUFr1NZPzv3 /cVGzMaBoeIeMtR4xoilPKcHtk2IHg3+T0sRj4pA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727963AbgBLOQv (ORCPT ); Wed, 12 Feb 2020 09:16:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:38212 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727665AbgBLOQv (ORCPT ); Wed, 12 Feb 2020 09:16:51 -0500 Received: from localhost (173-25-83-245.client.mchsi.com [173.25.83.245]) (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 6A51820714; Wed, 12 Feb 2020 14:16:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581517010; bh=EDVlPbawIuilZtpfWWUkGXCCUrkEzGW0hagfusO+Ufg=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=cXDtiZrqptolexiQhKMITEYPCSkhCzs1JTlKotTxklIhaTT8dhfuR7SgDy+d1Jf22 jAMiZ9KcprziYbeJgc9Nyziiu9lKsxI/Vc4bmci7t/5GsPFnjivO+iXX0AsPjzMSmn 3uj9ZWbFJE00XEArgyjIIbIQ98P05eWymejL7mA8= Date: Wed, 12 Feb 2020 08:16:49 -0600 From: Bjorn Helgaas To: Chen Yu Cc: Chen Yu , linux-pci@vger.kernel.org, Len Brown , "Rafael J. Wysocki" , Zhang Rui , Andy Shevchenko Subject: Re: [RFC][pci/pm] pci config space save restore issues during suspend/resume Message-ID: <20200212141649.GA130182@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200212062942.GA15014@chenyu-office.sh.intel.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 Wed, Feb 12, 2020 at 02:29:42PM +0800, Chen Yu wrote: > On Tue, Feb 11, 2020 at 07:50:43AM -0600, Bjorn Helgaas wrote: > > On Tue, Feb 11, 2020 at 01:57:06PM +0800, Chen Yu wrote: > > > Hi, > > > We found two issues in the code during suspend: > > > > > > 1. Andy Shevchenko found that, the save restore of pci config space > > > might cause potential issue. Current code uses > > > pci_read_config_dword() to read pci config header. However > > > hardware is not obliged to react correctly when trying to read > > > two/three 'adjacent' pci config registers with one dword read. > > > > > > Q1: Should we save/restore the pci config space header according > > > to the PCI spec strictly(pci_read_config_dword() for 32bit, > > > while pci_read_config_word() for 16bits, etc)? > > > > I'm sure you know my first question will be for a spec reference > > for this requirement that we read registers with the correct size > > :) If there is such a requirement, then of course we should > > follow it. > > > There seems to be no explicit request in the spec that the config > space header should be read according to each register's size. And > after recheck the PCI Express Base Specification, Rev. 4.0 Version > 1.0 pg703, it mentions: "An implemented 64-bit Base Address register > consumes two consecutive DWORD locations." It looks like content > within a DWORD io space should be adjacent. So > pci_read_config_dword() should be applicable. But this is just my > understanding, since we have not encountered issues caused by dword > reading yet, we might let it be for now. > > > > 2. The pci config space of some problematic devices(or due to firmware > > > bug) might become inaccessible after resumed from S3(suspend to > > > mem) on VM. > > > > > > Q2: Should we do sanity check on pci config space before saving > > > them? Say, invoke pci_dev_is_present() before suspend, if the > > > pci config space is not sane, bypass the config space saving > > > process, because there's no need to save invalid pci config > > > space. > > > > I'm not in favor of a sanity check, at least not yet. This sounds > > like a problem that has not been debugged yet. If the device is > > broken in some way, maybe a quirk would be appropriate. Otherwise, > > maybe there's some Linux issue in the resume from S3 path that we > > should fix. > > Got it. OK. Obviously you're tripping over some problem, but you haven't given any details about what it is, so I don't think there's anything I can help with yet. When you have a potential workaround patch or more details, don't hesitate to post them! Bjorn