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

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Date:   Thu, 2 Nov 2017 16:53:16 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>, freude@...ibm.com
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, heiko.carstens@...ibm.com, cohuck@...hat.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, qemu-s390x@...gnu.org,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com
Subject: Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest



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@...ux.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@...ux.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.