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

From: Pierre Morel
Date: Wed Aug 22 2018 - 12:03:57 EST

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?

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