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

Halil Pasic
2017-11-02T12:23:42Z

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 <akrowiak@linux.vnet.ibm.com> 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 <akrowiak@linux.vnet.ibm.com>
>>> ---
>>> 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