Messages in this thread | | | Subject | Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure control domains | From | Tony Krowiak <> | Date | Wed, 22 Aug 2018 15:16:19 -0400 |
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On 08/22/2018 01:11 PM, Halil Pasic wrote: > > > On 08/22/2018 05:48 PM, Christian Borntraeger wrote: >> On 08/22/2018 05:34 PM, Pierre Morel wrote: >>> On 22/08/2018 17:11, Christian Borntraeger wrote: >>>> >>>> >>>> On 08/22/2018 01:03 PM, Pierre Morel wrote: >>>>>> That's interesting. >>>>>> >>>>>>> IMHO this quote is quite a half-full half-empty cup one: >>>>>>> * it mandates the set of usage domains is a subset of the set >>>>>>> of the control domains, but >>>>>>> * it speaks of independent controls, namely about the 'usage >>>>>>> domain index' >>>>>>> and the 'control domain index list' and makes the enforcement of >>>>>>> the rule >>>>>>> a job of the administrator (instead of codifying it in the >>>>>>> controls). >>>>>> I'm wondering if a configuration with a usage domain that is not >>>>>> also a >>>>>> control domain is rejected outright? Anybody tried that? :) >>>>> >>>>> Yes, and no it is not. >>>>> We can use a queue (usage domain) to a AP card for SHA-512 or RSA >>>>> without >>>>> having to define the queue as a control domain. >>>> >>>> Huh? My HMC allows to add a domain as >>>> - control only domain >>>> - control and usage domain. >>>> >>>> But I am not able to configure a usage-only domain for my LPAR. >>>> That seems to match >>>> the current code, no? >>>> >>> >>> Yes, it may not be configurable by the HMC but if we start a guest >>> with no control domain it is not a problem to access the hardware >>> through the usage domain. >>> >>> I tested this a long time ago, but tested again today to be sure on >>> my LPAR. >>> >>> AFAIU adding a control only domain and a control and usage domain >>> allows say: >>> control and usage domain 1 >>> control only domain 2 >>> >>> Allow to send a message to domain 2 using queue 1 >>> >>> Allow also to send a domain modifying message to domain 1 using queue 1 >>> >>> control domain are domain which are controlled >> >> So you have changed the code to not automatically make a usage domain a >> control domain in the bitfield (and you could still use it as a usage >> domain). Correct? > > I tested basically the same yesterday, with the same results. > >> I think this is probably expected. the "usage implies control" seems to >> be a convention implemented by HMC (lpar) and z/VM but millicode offers >> the bits to have usage-only domains. As LPAR and z/VM will always enable >> any usage-domain to also be a control domain we should do the same. > > I'm fine either way, but slightly prefer higher level management software > and not the kernel accommodating this convention. > > Please consider a quote from Harald's mail in another sub-thread > > > """ > ... about control domains > > Talked with the s390 firmware guys. The convention that the control > domain > mask is a superset of the usage domain mask is only true for 1st level > guests. > > It is absolutely valid to run a kvm guest with restricted control domain > mask bitmap in the CRYCB. It is valid to have an empty control domain > mask > and the guest should be able to run crypto CPRBs on the usage > domain(s) without > any problems. However, nobody has tried this. > """ > > I'm yet to get an explanation why was this convention established in > the first > place. And I can not figure it out myself. For me a setup where I know > that > the domains used by some guest can not be modified by the same guest > makes > perfect sense. If I try to think in analogies, I kind of compare > modification > (that is control domain) with write access, and usage (that is usage > domain) > with read access to, let's say a regular file. For me, all options > (rw, r, and w) > do make sense, and if I had to pick the one that makes the least sense > I would > pick write only. The convention is in these terms making read-only > illegal. But > should 'usage only domains' ever get identified as something somebody > wants to do > we can just add an attribute for that. So I'm fine either way.
One of the things I suggested in a private conversation with Christian earlier today was to provide an additional rw sysfs attribute - a boolean - that indicates whether all usage domains should also be control domains. The default could be true. This would allow one to configure guests with usage-only domains as well as satisfy the convention.
> > > Still I find the commit message for this patch, the implementation of > assign_control_domain() and also the documentation slightly misleading > regarding > what does one get from assign_domain.
> > > Regards, > Halil > > > > > >> >> >>> It seems that the HMC enforce the LPARs to have access to their >>> usage domain (AFAIU from Harald) >>
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