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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 1B0CBC43387 for ; Wed, 2 Jan 2019 15:59:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D0FB521903 for ; Wed, 2 Jan 2019 15:59:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729748AbfABP73 (ORCPT ); Wed, 2 Jan 2019 10:59:29 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:40794 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729119AbfABP73 (ORCPT ); Wed, 2 Jan 2019 10:59:29 -0500 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x02FxDYp133365 for ; Wed, 2 Jan 2019 10:59:28 -0500 Received: from e06smtp03.uk.ibm.com (e06smtp03.uk.ibm.com [195.75.94.99]) by mx0a-001b2d01.pphosted.com with ESMTP id 2prwpaftwh-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 02 Jan 2019 10:59:28 -0500 Received: from localhost by e06smtp03.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 2 Jan 2019 15:59:21 -0000 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x02FxKck58654824 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 2 Jan 2019 15:59:20 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9D8F911C05B; Wed, 2 Jan 2019 15:59:20 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 487C211C04A; Wed, 2 Jan 2019 15:59:20 +0000 (GMT) Received: from oc2783563651 (unknown [9.152.224.118]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 2 Jan 2019 15:59:20 +0000 (GMT) Date: Wed, 2 Jan 2019 16:59:19 +0100 From: Halil Pasic To: Cornelia Huck Cc: "Wang, Wei W" , Christian Borntraeger , "virtio-dev@lists.oasis-open.org" , "linux-kernel@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "mst@redhat.com" , "pbonzini@redhat.com" , "dgilbert@redhat.com" Subject: Re: [virtio-dev] RE: [PATCH v1 0/2] Virtio: fix some vq allocation issues In-Reply-To: <20190102142338.15bfe876.cohuck@redhat.com> References: <1545963986-11280-1-git-send-email-wei.w.wang@intel.com> <286AC319A985734F985F78AFA26841F73DEEA8E9@shsmsx102.ccr.corp.intel.com> <20181230070600.512bbb8b@oc2783563651> <286AC319A985734F985F78AFA26841F73DEEC8DF@shsmsx102.ccr.corp.intel.com> <20190101004019.7f20aafa@oc2783563651> <20190102105314.0b4e2485.cohuck@redhat.com> <20190102142338.15bfe876.cohuck@redhat.com> Organization: IBM X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19010215-0012-0000-0000-000002E0896C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19010215-0013-0000-0000-00002117466E Message-Id: <20190102165919.0cd9365a@oc2783563651> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-01-02_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901020144 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2 Jan 2019 14:23:38 +0100 Cornelia Huck wrote: > On Wed, 2 Jan 2019 10:53:14 +0100 > Cornelia Huck wrote: > > > On Tue, 1 Jan 2019 00:40:19 +0100 > > Halil Pasic wrote: > > > > As I said, at the moment I don't have a preference regarding the fix, > > > partly because I'm not sure if "reading config inside the handler" is OK > > > or not. Maybe Connie or Michael can help us here. I'm however sure that > > > commit 86a5597 "virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT" > > > breaks virtio-balloon with the ccw transport (i.e. effectively breaks > > > virtio-balloon on s390): it used to work before and does not work > > > after. > > > > Yes, that's unfortunate. > > > > > > > > AFAICT tweaking the balloon code may be simpler than tweaking the > > > virtio-ccw (transport code). ccw_io_helper() relies on getting > > > an interrupt when the issued IO is done. If virtio-ccw is buggy, it > > > needs to be fixed, but I'm not sure it is. > > > > I would not call virtio-ccw buggy, but it has some constraints that > > virtio-pci apparently doesn't have (and which did not show up so far; > > e.g. virtio-blk schedules a work item on config change, so there's no > > deadlock there.) > > > > One way to get out of that constraint (don't interact with the config > > space directly in the config changed handler) would be to schedule a > > work item in virtio-ccw that calls virtio_config_changed() for the > > device. My understanding is that delaying the notification to a work > > queue would be fine. > > Unfortunately, calling virtio_config_changed() from a work item is not > enough: That function takes the config_lock, and the virtio-ccw code to > get the config both needs to allocate some memory and call schedule :/ > > The best option really seems to be > - have virtio-balloon move the handling of the config change onto a > workqueue or something like that, and > - document that you cannot read/write the virtio config space from an > atomic context > > Unless someone has a better idea? > I wonder, would making config_lock a mutex suffice? I've already hinted that a virtio-balloon side fix is probably the simpler variant. I agree, let's fix the regression first, and think about wether to teach virtio-ccw to allow config manipulation from virtio_config_changed() or not later. Regards, Halil