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=-7.0 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 2E2E8C06511 for ; Mon, 1 Jul 2019 12:09:49 +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 0A9CC20B7C for ; Mon, 1 Jul 2019 12:09:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A9CC20B7C 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]:58040 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hhv80-000510-CA for qemu-devel@archiver.kernel.org; Mon, 01 Jul 2019 08:09:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52264) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hhv2c-0001Im-OH for qemu-devel@nongnu.org; Mon, 01 Jul 2019 08:04:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hhv2a-0001Hz-PY for qemu-devel@nongnu.org; Mon, 01 Jul 2019 08:04:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55735) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hhv2Y-0001EG-Qk for qemu-devel@nongnu.org; Mon, 01 Jul 2019 08:04:12 -0400 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 4269AC0B91AB for ; Mon, 1 Jul 2019 12:04:08 +0000 (UTC) Received: from localhost (unknown [10.43.2.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9670B1001B19; Mon, 1 Jul 2019 12:04:07 +0000 (UTC) Date: Mon, 1 Jul 2019 14:04:02 +0200 From: Igor Mammedov To: "Michael S. Tsirkin" Message-ID: <20190701140402.6647a3a4@redhat.com> In-Reply-To: <20190701051959-mutt-send-email-mst@kernel.org> References: <20190621064615.20099-1-mst@redhat.com> <20190621064615.20099-4-mst@redhat.com> <20190625150730.31d9d699@redhat.com> <20190701051959-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 [10.5.110.32]); Mon, 01 Jul 2019 12:04:08 +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 Mon, 1 Jul 2019 05:20:41 -0400 "Michael S. Tsirkin" wrote: > On Tue, Jun 25, 2019 at 03:07:30PM +0200, Igor Mammedov wrote: > > 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? > > You are missing the underscore. > > slt_sta is the old value. > sltsta is the new value. I did notice it but still don't see where exp_cap + PCI_EXP_SLTSTA is being modified in call chain between pcie_cap_slot_get(d, &slt_ctl, &slt_sta) ... pcie_cap_slot_write_config(): sltsta = pci_get_word(exp_cap + PCI_EXP_SLTSTA) > > > > + pci_set_word(exp_cap + PCI_EXP_SLTSTA, sltsta); > > > + } > > > hotplug_event_clear(dev); > > > } > > > >