Re: [PATCH v9 12/22] s390: vfio-ap: sysfs interfaces to configure control domains

[Pierre Morel]

On 22/08/2018 17:48, 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?

yes
and I used Harald's libica tests to verify it in the guest.

> 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.
>
>
> > It seems that the HMC enforce the LPARs to have access to their usage domain (AFAIU from Harald)


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany