On Tue, 3 Jul 2018 15:58:37 +0200 Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > On 07/03/2018 03:25 PM, Cornelia Huck wrote: > > On Tue, 3 Jul 2018 14:20:11 +0200 > > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > >> On 07/03/2018 01:52 PM, Cornelia Huck wrote: > >>> On Tue, 3 Jul 2018 11:22:10 +0200 > >>> Halil Pasic <pasic@xxxxxxxxxxxxx> 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? > > > > I don't think block devices (which are designed to be more or less > > permanently accessed, e.g. by mounting a file system) have the same > > semantics as ap devices (which exist as a backend for crypto requests). > > Not everything that makes sense for a block device makes sense for > > other devices as well, and I don't think it makes sense here. > > > > I'm still confused. If it's about frequency of access (as hinted > by block devices accessed more or less permanently) I'm not sure > there is a substantial difference. I guess there are scenarios where > the AP domain is used very seldom (e.g. protected keys --> most of > the crypto ops done by CPACF but AP unwraps at the beginning), but > there are such scenarios for block too. > > If it's about (persistent) state, I guess it again depends on the > scenario and on the type of the card. But I may be wrong. So, let's turn this around: Why do you think that dasd (and not qeth or whatever) is a good model for ap device unbinding? Because I really fail to get it... maybe the ap driver maintainers can chime in. > > >> > >>>> 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. > > > > If the current implementation of vfio-ap cannot deal with it (by > > cleaning up, blocking, etc.), it needs at the very least be documented > > so that it can be implemented later. I do not know what the SIE will or > > won't do to assist here (e.g., if you're removing it from some masks, > > the device will already be inaccessible to the guest). But the part you > > were referring to was talking about the existing host driver anyway, > > wasn't it? > > > > I was thinking about both directions. Re-classifying a device form > pass-through to normal should also be possible. But the document only > talks about one direction. Presumably because it (rightfully) focuses on setting up vfio-ap? > > I'm not familiar with the existing host drivers. If we can say 'Hey, > unbind is perfectly safe at any time: no per-cautions need to be considered!' > I'm very happy with that. Although I would find it a bit surprising. > > I just wanted to make sure this is not something we forget. > > >> > >> 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. > > > > I'd assume "know which devices are for the host and which devices are > > for the guests" to be a given, no? > > > > My other email scratches this topic. AFAIK we don't have a solution for > that yet. Nor we have a good understanding of how and to what extent > is statically given what is given. E.g. if one wants to re-partition my AP > resources (and at some point one will have to at least do the initial > re-partitioning) do I need a reboot for the changes to take effect? Or > is this 'known' variable during the uptime of an OS. I think that is really out of scope for this file, which I'd expect to explain how vfio-ap basically works and which incantations I need to give crypto devices to a guest. It should NOT focus on administrative tasks; this should either be delegated to the likes of libvirt or documented in a "how to use crypto cards with kvm" kind of technical writeup. If there's a limitation (e.g. you can't easily unbind again), write a line here.
