Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752604AbdLEPBw (ORCPT ); Tue, 5 Dec 2017 10:01:52 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:45450 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752484AbdLEPBt (ORCPT ); Tue, 5 Dec 2017 10:01:49 -0500 Subject: Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest To: Cornelia Huck , Harald Freudenberger Cc: Christian Borntraeger , Martin Schwidefsky , freude@de.ibm.com, pmorel@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, pasic@linux.vnet.ibm.com, Boris Fiuczynski , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, heiko.carstens@de.ibm.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, alifm@linux.vnet.ibm.com, qemu-s390x@nongnu.org, jjherne@linux.vnet.ibm.com, thuth@redhat.com References: <1507916344-3896-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1507916344-3896-20-git-send-email-akrowiak@linux.vnet.ibm.com> <20171016112510.39e9c330@mschwideX1> <3e836f59-3ef1-57d8-d6df-b66011c173c4@de.ibm.com> <6d9ae0c1-6f64-1562-bf10-864cf66e3a08@de.ibm.com> <40cdab64-9eeb-02bd-f260-80e9da8c9034@linux.vnet.ibm.com> <35f17b01-49e0-eafb-ad05-c642c579dd3a@de.ibm.com> <8c8c7a0e-2ae4-443b-9444-e2022436c3ee@linux.vnet.ibm.com> <20171205150421.01ec1ed8.cohuck@redhat.com> From: Tony Krowiak Date: Tue, 5 Dec 2017 10:01:31 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20171205150421.01ec1ed8.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-TM-AS-GCONF: 00 x-cbid: 17120515-0024-0000-0000-000002FD1EE5 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008153; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000243; SDB=6.00955814; UDB=6.00483111; IPR=6.00735851; BA=6.00005729; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018362; XFM=3.00000015; UTC=2017-12-05 15:01:37 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17120515-0025-0000-0000-0000463AD827 Message-Id: <7557ad65-48dd-9a82-2988-8a124d765939@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-05_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712050217 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3744 Lines: 63 On 12/05/2017 09:04 AM, Cornelia Huck wrote: > On Tue, 5 Dec 2017 08:52:57 +0100 > Harald Freudenberger wrote: > >> On 12/02/2017 02:30 AM, Tony Krowiak wrote: >>> I agree with your suggestion that defining a new CPU model feature is probably >>> the best way to resolve this issue. The question is, should we define a single >>> feature indicating whether AP instructions are installed and set features bits >>> for the guest based on whether or not they are set in the linux host, or should >>> we define additional CPU model features for turning features bits on and off? >>> I guess it boils down to what behavior is expected for the AP bus running on >>> the linux guest. Here is a rundown of the facilities bits associated with AP >>> and how they affect the behavior of the AP bus: >>> >>> * STFLE.12 indicates whether the AP query function is available. If this bit >>> is not set, then the AP bus scan will only test domains 0-15. For example, >>> if adapters 4, 5, and 6 and domains 12 and 71 (0x47) are installed, then AP >>> queues 04.0047, 05.0047 and 06.0047 will not be made available. >> STFLE 12 is the indication for Query AP Configuration Information (QCI) available. >>> * STFLE.15 indicates whether the AP facilities test function is available. If >>> this bit is not set, then the CEX4, CEX5 and CEX6 device drivers discovered >>> by the AP bus scan will not get bound to any AP device drivers. Since the >>> AP matrix model supports only CEX4 and greater, no devices will be bound >>> to any driver for a guest. >> This T-Bit extension to the TAPQ subfunction is a must have. When kvm only >> supports CEX4 and upper then this bit could also act as the indicator for >> AP instructions available. Of course if you want to implement pure virtual >> full simulated AP without any real AP hardware on the host this bit can't >> be the indicator. > It would probably make sense to group these two together. Or is there > any advantage in supporting only a part of it? After thinking about this a little more, I've come to the conclusion that all of this might be moot for the following reasons: * If STFLE.12 is not set for the linux host, then AP bus scan running on the host will not detect any domains with a domain number higher than 15, so no AP queues with a queue index higher than 15 will be available to bind to the vfio_ap_matrix driver. Consequently, no domain higher than 15 can be assigned to any guest. In this case, the AP bus scan running on the guest will never detect a domain higher than 15, regardless of the setting of STFLE.12 for the guest. * If STFLE.15 is not set for the linux host, then then there will be no CEX4, CEX5 or CEX6 queues available to bind to the vfio_ap_matrix driver, so no AP adapters or domains can be assigned to any KVM guest. The bottom line is the STFLE bit settings for the linux host will control what APs are available to the KVM guest. Since STFLE.15 controls whether any CEX4,5 or 6 devices are even available, I think this bit can be combined into the feature that indicates whether AP is available. As long as AP instructions are available on the linux host, I'm not sure whether STFLE.12 needs a feature at all. > >>> * STFLE.65 indicates whether AP interrupts are available. If this bit is not >>> set, then the AP bus will use polling instead of using interrupt handlers >>> to process AP events. > So, does this indicate "adapter interrupts for AP" only? If so, we > should keep this separate and only enable it when we have the gisa etc. > ready. Yes, this indicates AP interrupts only. The plan is to enable this when GISA is available and we can implement interrupt processing. >