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

Christian Borntraeger
2017-11-02T12:08:17Z

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.