From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751565AbeDXQmq (ORCPT ); Tue, 24 Apr 2018 12:42:46 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57950 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750827AbeDXQmo (ORCPT ); Tue, 24 Apr 2018 12:42:44 -0400 Subject: Re: [PATCH 01/10] vfio: ccw: Moving state change out of IRQ context To: Cornelia Huck , Pierre Morel Cc: Dong Jia Shi , pasic@linux.vnet.ibm.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1524149293-12658-1-git-send-email-pmorel@linux.vnet.ibm.com> <1524149293-12658-2-git-send-email-pmorel@linux.vnet.ibm.com> <20180424065442.GV12194@bjsdjshi@linux.vnet.ibm.com> <20180424115929.5b5e1ff0.cohuck@redhat.com> From: Halil Pasic Date: Tue, 24 Apr 2018 18:42:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180424115929.5b5e1ff0.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18042416-0040-0000-0000-000004326CA7 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18042416-0041-0000-0000-000026369C86 Message-Id: <245ee547-75bc-95f5-5acb-bfa96f91afd2@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-24_04:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804240159 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/24/2018 11:59 AM, Cornelia Huck wrote: > On Tue, 24 Apr 2018 10:40:56 +0200 > Pierre Morel wrote: > >> On 24/04/2018 08:54, Dong Jia Shi wrote: >>> * Pierre Morel [2018-04-19 16:48:04 +0200]: >>> >>> [...] >>> >>>> @@ -94,9 +83,15 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) >>>> static void vfio_ccw_sch_irq(struct subchannel *sch) >>>> { >>>> struct vfio_ccw_private *private = dev_get_drvdata(&sch->dev); >>>> + struct irb *irb = this_cpu_ptr(&cio_irb); >>>> >>>> inc_irq_stat(IRQIO_CIO); >>>> - vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_INTERRUPT); >>>> + memcpy(&private->irb, irb, sizeof(*irb)); >>>> + >>>> + WARN_ON(work_pending(&private->io_work)); >>> Hmm, why do we need this? >> >> The current design insure that we have not two concurrent SSCH requests. >> How ever I want here to track spurious interrupt. >> If we implement cancel, halt or clear requests, we also may trigger (AFAIU) >> a second interrupts depending on races between instructions, controller >> and device. > > You won't get an interrupt for a successful cancel. If you do a > halt/clear, you will make the subchannel halt/clear pending in addition > to start pending and you'll only get one interrupt (if the I/O has > progressed far enough, you won't be able to issue a hsch). The > interesting case is: > - guest does a ssch, we do a ssch on the device > - the guest does a csch before it got the interrupt for the ssch > - before we do the csch on the device, the subchannel is already status > pending with completion of the ssch > - after we issue the csch, we get a second interrupt (for the csch) > > I think we should present two interrupts to the guest in that case. > Races between issuing ssch/hsch/csch and the subchannel becoming status > pending happen on real hardware as well, we're just more likely to see > them with the vfio layer in between. > AFAIU this will be the problem of the person implementing the clear and the halt for vfio-ccw. I.e. it's a non-problem right now. > (I'm currently trying to recall what we're doing with unsolicited > interrupts. These are fun wrt deferred cc 1; I'm not sure if there are > cases where we want to present a deferred cc to the guest.) What are 'fun wrt deferred cc 1' again? The deferred cc I understand but wrt does not click at all. > > Also, doing a second ssch before we got final state for the first one > is perfectly valid. Linux just does not do it, so I'm not sure if we > should invest too much time there. > >> >> We do not need it strongly. >> >>> >>>> + queue_work(vfio_ccw_work_q, &private->io_work); >>>> + if (private->completion) >>>> + complete(private->completion); >>>> } >>>> >>>> static int vfio_ccw_sch_probe(struct subchannel *sch) >>> [...] >>> >> >