Re: [qemu-s390x] [RFC 19/19] s390/facilities: enable AP facilities needed by guest

[Halil Pasic]

On 11/02/2017 01:08 PM, Christian Borntraeger wrote:
> 
> 
> On 10/16/2017 11:25 AM, Martin Schwidefsky wrote:
>> On Fri, 13 Oct 2017 13:39:04 -0400
>> Tony Krowiak <address@hidden> wrote:
>>
>>> Sets up the following facilities bits to enable the specified AP
>>> facilities for the guest VM:
>>>     * STFLE.12: Enables the AP Query Configuration Information
>>>                 facility. The AP bus running in the guest uses
>>>                 the information returned from this instruction
>>>                 to configure AP adapters and domains for the
>>>                 guest machine.
>>>     * STFLE.15: Indicates the AP facilities test is available.
>>>                 The AP bus running in the guest uses the
>>>                 information.
>>>
>>> Signed-off-by: Tony Krowiak <address@hidden>
>>> ---
>>>  arch/s390/tools/gen_facilities.c |    2 ++
>>>  1 files changed, 2 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/s390/tools/gen_facilities.c 
>>> b/arch/s390/tools/gen_facilities.c
>>> index 70dd8f1..eeaa7db 100644
>>> --- a/arch/s390/tools/gen_facilities.c
>>> +++ b/arch/s390/tools/gen_facilities.c
>>> @@ -74,8 +74,10 @@ struct facility_def {
>>>                     8,  /* enhanced-DAT 1 */
>>>                     9,  /* sense-running-status */
>>>                     10, /* conditional sske */
>>> +                   12, /* AP query configuration */
>>>                     13, /* ipte-range */
>>>                     14, /* nonquiescing key-setting */
>>> +                   15, /* AP special-command facility */
>>>                     73, /* transactional execution */
>>>                     75, /* access-exception-fetch/store indication */
>>>                     76, /* msa extension 3 */
>>
>> With this all KVM guests will always have the AP instructions available, no?
>> In principles I like this approach, but it differs from the way z/VM does 
>> things,
>> there the guest will get an exception if it tries to execute an AP 
>> instruction
>> if there are no AP devices assigned to the guest. I wonder if there is a 
>> reason
>> why z/VM does it the way it does.
> 
> A good question. For LPAR it seems that you have AP instructions even if you 
> have
> no crypto cards.
> 

I've tried to figure these things out last week but I've failed.

Right at the beginning of  AR-10334-03-POK we have this text:
"An adjunct processor (AP) facility consists of the three AP
instructions, and one to sixty-four APs.". This reads like if we
have AP facility we have to have at least one AP.

But when I've tried to get a better understanding how the
presence/absence of the AP facility is indicated and what facility
bits do we have in this context I got confused.

Tony, could you please give us a detailed summary on this (best with
references, and focusing on the (guest) program perspective)?

Regards,
Halil