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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,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 61126C48BD4 for ; Tue, 25 Jun 2019 13:22:19 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 307DB208CA for ; Tue, 25 Jun 2019 13:22:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 307DB208CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60122 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hflOs-0002qN-F9 for qemu-devel@archiver.kernel.org; Tue, 25 Jun 2019 09:22:18 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51018) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hflAi-0001IG-12 for qemu-devel@nongnu.org; Tue, 25 Jun 2019 09:07:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hflAg-0007yl-W7 for qemu-devel@nongnu.org; Tue, 25 Jun 2019 09:07:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60766) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hflAg-0007y5-Hn for qemu-devel@nongnu.org; Tue, 25 Jun 2019 09:07:38 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 78F613082A24 for ; Tue, 25 Jun 2019 13:07:37 +0000 (UTC) Received: from localhost (unknown [10.43.2.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id F30595D9D3; Tue, 25 Jun 2019 13:07:34 +0000 (UTC) Date: Tue, 25 Jun 2019 15:07:30 +0200 From: Igor Mammedov To: "Michael S. Tsirkin" Message-ID: <20190625150730.31d9d699@redhat.com> In-Reply-To: <20190621064615.20099-4-mst@redhat.com> References: <20190621064615.20099-1-mst@redhat.com> <20190621064615.20099-4-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 25 Jun 2019 13:07:37 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 3/3] pcie: work around for racy guest init X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, 21 Jun 2019 02:46:50 -0400 "Michael S. Tsirkin" wrote: > During boot, linux guests tend to clear all bits in pcie slot status > register which is used for hotplug. > If they clear bits that weren't set this is racy and will lose events: > not a big problem for manual hotplug on bare-metal, but a problem for us. > > For example, the following is broken ATM: > > /x86_64-softmmu/qemu-system-x86_64 -enable-kvm -S -machine q35 \ > -device pcie-root-port,id=pcie_root_port_0,slot=2,chassis=2,addr=0x2,bus=pcie.0 \ > -device virtio-balloon-pci,id=balloon,bus=pcie_root_port_0 \ > -monitor stdio disk.qcow2 > (qemu)device_del balloon > (qemu)cont > > Balloon isn't deleted as it should. > > As a work-around, detect this attempt to clear slot status and revert > status to what it was before the write. > > Note: in theory this can be detected as a duplicate button press > which cancels the previous press. Does not seem to happen in > practice as guests seem to only have this bug during init. > > Note2: the right thing to do is probably to fix Linux to > read status before clearing it, and act on the bits that are set. > > Signed-off-by: Michael S. Tsirkin > --- > hw/pci/pcie.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c > index f8490a00de..c605d32dd4 100644 > --- a/hw/pci/pcie.c > +++ b/hw/pci/pcie.c > @@ -610,6 +610,25 @@ void pcie_cap_slot_write_config(PCIDevice *dev, uint16_t slt_ctl, uint16_t slt_s > uint16_t sltsta = pci_get_word(exp_cap + PCI_EXP_SLTSTA); > > if (ranges_overlap(addr, len, pos + PCI_EXP_SLTSTA, 2)) { > + /* > + * Guests tend to clears all bits during init. > + * If they clear bits that weren't set this is racy and will lose events: > + * not a big problem for manual button presses, but a problem for us. > + * As a work-around, detect this and revert status to what it was > + * before the write. > + * > + * Note: in theory this can be detected as a duplicate button press > + * which cancels the previous press. Does not seem to happen in > + * practice as guests seem to only have this bug during init. > + */ > +#define PCIE_SLOT_EVENTS (PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD | \ > + PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_PDC | \ > + PCI_EXP_SLTSTA_CC) > + > + if (val & ~slt_sta & PCIE_SLOT_EVENTS) { > + sltsta = (sltsta & ~PCIE_SLOT_EVENTS) | (slt_sta & PCIE_SLOT_EVENTS); I'm reading it as: sltsta = LOWER_PART(sltsta) | UPPER_PART(sltsta) which basically sltsta = sltsta or am I missing something here? > + pci_set_word(exp_cap + PCI_EXP_SLTSTA, sltsta); > + } > hotplug_event_clear(dev); > } >