Messages in this thread | | | Subject | Re: [PATCH v6 21/21] s390: doc: detailed specifications for AP virtualization | From | Halil Pasic <> | Date | Tue, 3 Jul 2018 14:20:11 +0200 |
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On 07/03/2018 01:52 PM, Cornelia Huck wrote: > On Tue, 3 Jul 2018 11:22:10 +0200 > Halil Pasic <pasic@linux.ibm.com> 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
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