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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 8656DC5CFFE for ; Tue, 11 Dec 2018 19:01:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5ABAB2087F for ; Tue, 11 Dec 2018 19:01:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5ABAB2087F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726836AbeLKTBS (ORCPT ); Tue, 11 Dec 2018 14:01:18 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59716 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726329AbeLKTBP (ORCPT ); Tue, 11 Dec 2018 14:01:15 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9ECDC46202; Tue, 11 Dec 2018 19:01:14 +0000 (UTC) Received: from redhat.com (ovpn-126-162.rdu2.redhat.com [10.10.126.162]) by smtp.corp.redhat.com (Postfix) with SMTP id AB46A103BAB7; Tue, 11 Dec 2018 19:01:13 +0000 (UTC) Date: Tue, 11 Dec 2018 14:01:13 -0500 From: "Michael S. Tsirkin" To: Bjorn Helgaas Cc: linux-kernel@vger.kernel.org, xuyandong , stable@vger.kernel.org, Yinghai Lu , Jesse Barnes , linux-pci@vger.kernel.org Subject: Re: [PATCH] pci: avoid bridge feature re-probing on hotplug Message-ID: <20181211135755-mutt-send-email-mst@kernel.org> References: <20181211021617.24072-1-mst@redhat.com> <20181211141808.GE99796@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181211141808.GE99796@google.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Tue, 11 Dec 2018 19:01:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 11, 2018 at 08:18:08AM -0600, Bjorn Helgaas wrote: > Hi Michael, > > Please run "git log --oneline drivers/pci/setup-bus.c" and follow > the usual style. > > On Mon, Dec 10, 2018 at 09:18:40PM -0500, Michael S. Tsirkin wrote: > > commit 1f82de10d6 ("PCI/x86: don't assume prefetchable ranges are > > 64bit") added probing of bridge support for 64 bit memory > > each time bridge is re-enumerated. > > Use conventional SHA1 reference (12-char SHA1). > > > Unfortunately this probing is destructive if any device behind > > the bridge is in use at this time. > > Agreed, this sounds like a problem. > > > There's no real need to re-probe the bridge features as the > > regiters in question never change - detect that using > > the memory flag being set and skip the probing. > > s/regiters/registers/ Will address above. > > Avoiding repeated calls to pci_bridge_check_ranges might be even nicer > > would be a bigger patch and probably not appropriate on stable. > > Maybe so. The ideal thing might be to have a trivial patch like this > that can be marked for stable, immediately followed by the nicer > patch. Trivial band-aids tend to accumulate and make things harder in > the future. I understand, and I looked at it briefly, but it's not a simple change, with probing taking detours through acpi etc. I plan to look at it some more but should we release another linux with this bug? > I'd have to take a much harder look at the problem to understand > 1f82de10d6b1. The comment about "double check" seems misleading -- as > you say, the hardware doesn't change and checking once should be > enough. And if we're calling pci_bridge_check_ranges() more than > necessary, that sounds like a problem, too. So that will kind of make it a non issue. Should we still worry? > > Reported-by: xuyandong > > Cc: stable@vger.kernel.org > > Cc: Yinghai Lu > > Cc: Jesse Barnes > > Signed-off-by: Michael S. Tsirkin > > --- > > > > This issue has been reported on upstream Linux and Centos. > > Are there URLs to these reports that we could include in the changelog? https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg01711.html and specifically https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg02082.html > > drivers/pci/setup-bus.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c > > index ed960436df5e..7ab42f76579e 100644 > > --- a/drivers/pci/setup-bus.c > > +++ b/drivers/pci/setup-bus.c > > @@ -741,6 +741,13 @@ static void pci_bridge_check_ranges(struct pci_bus *bus) > > struct resource *b_res; > > > > b_res = &bridge->resource[PCI_BRIDGE_RESOURCES]; > > + > > + /* Don't re-check after this was called once already: > > + * important since bridge might be in use. > > + */ > > + if (b_res[1].flags & IORESOURCE_MEM) > > + return; > > Use conventional multi-line comment style. > > This test isn't 100%: devices below the bridge could be using only IO, > or theoretically could be even using just config space. > > If it's safe to bail out if the bridge is in use, why isn't it safe to > bail out *always*? > > > b_res[1].flags |= IORESOURCE_MEM; > > > > pci_read_config_word(bridge, PCI_IO_BASE, &io); > > -- > > MST