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

Tony Krowiak
2017-11-02T18:49:12Z

On 11/02/2017 11:53 AM, Christian Borntraeger wrote:
>
> 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.
The ECA.28 bit controls whether instructions are intercepted or
interpreted - i.e., handled via hardware
virtualization. If set, as is done in patch2, then instructions will be
interpreted. I don't see how
that affects enabling or disabling AP instructions, unless we don't set
ECA.28, intercept every instruction
and program check. Am I missing something here?
>