From mboxrd@z Thu Jan 1 00:00:00 1970 From: Halil Pasic Subject: Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization Date: Tue, 3 Jul 2018 14:20:11 +0200 Message-ID: <18532145-abeb-1251-926e-edbc6fa0bcb0@linux.ibm.com> References: <1530306683-7270-1-git-send-email-akrowiak@linux.vnet.ibm.com> <1530306683-7270-22-git-send-email-akrowiak@linux.vnet.ibm.com> <49b11ac2-2230-ad74-1583-c6a57f8b31e3@linux.ibm.com> <6a330cae-2fe2-54df-edce-c3360117cf3c@linux.ibm.com> <13998e79-9bae-5c55-b83d-85e6db8d3b99@linux.ibm.com> <20180703135205.2ebb107f.cohuck@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Harald Freudenberger , Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, kwankhede@nvidia.com, bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com, alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com, alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, thuth@redhat.com, pasic@linux.vnet.ibm.com, berrange@redhat.com, fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com, Tony Krowiak To: Cornelia Huck Return-path: In-Reply-To: <20180703135205.2ebb107f.cohuck@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 07/03/2018 01:52 PM, Cornelia Huck wrote: > On Tue, 3 Jul 2018 11:22:10 +0200 > Halil Pasic wrote: > [..] >> >> Let me try to invoke the DASD analogy. If one for some reason wants to detach >> a DASD the procedure to follow seems to be (see >> https://www.ibm.com/support/knowledgecenter/en/linuxonibm/com.ibm.linux.z.lgdd/lgdd_t_dasd_online.html) >> the following: >> 1) Unmount. >> 2) Offline possibly using safe_offline. >> 3) Detach. >> >> Detaching a disk that is currently doing I/O asks for trouble, so the admin is encouraged >> to make sure there is no pending I/O. > > I don't think we can use dasd (block devices) as a good analogy for > every kind of device (for starters, consider network devices). > I did not use it for every kind of device. I used it for AP. I'm under the impression you find the analogy inappropriate. If, could you please explain why? >> In case of AP you can interpret my 'in use' as the queue is not empty. In my understanding >> unbind is supposed to be hard (I used the word radical). That's why I compared it to pulling >> a cable. So that's why I ask is there stuff the admin is supposed to do before doing the >> unbind. > > Are you asking for a kind of 'quiescing' operation? I would hope that > the crypto drivers already can deal with that via flushing the queue, > not allowing new requests, or whatever. This is not the block device > case. > The current implementation of vfio-ap which is a crypto driver too certainly can not deal 'with that'. Whether the rest of the drivers can, I don't know. Maybe Tony can tell. I'm aware of the fact that AP adapters are not block devices. But as stated above I don't understand what is the big difference regarding the unbind operation. > Anyway, this is an administrative issue. If you don't have a clear > concept which devices are for host usage and which for guest usage, you > already have problems. I'm trying to understand the whole solution. I agree, this is an administrative issue. But the document is trying to address such administrative issues. > > Speaking of administrative issues, is there libvirt support for vfio-ap > under development? It would be helpful to validate the approach. I full-heartedly agree. I guess Tony will have to answer this one too. Regards, Halil