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

Christian Borntraeger
2017-11-02T15:53:16Z

On 11/02/2017 04:36 PM, Tony Krowiak wrote:
> On 11/02/2017 08:08 AM, 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 don't believe these facilities control whether or not AP instructions will be available
>
> to the guest.

This is actually handled by your patch2 enabling the ECA bit.
I think we must decide if we want to be able to disable these instructions
via the cpu model. If yes we must then couple the facilities with the enablement.