linux-kernel - Re: [PATCH 16/32] KVM: s390: expose the guest zPCI interpretation facility

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Message-ID: <c076f524-8d47-c9aa-9033-cf7658c4f102@linux.ibm.com>
Date:   Fri, 17 Dec 2021 12:13:28 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        vneethv@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/32] KVM: s390: expose the guest zPCI interpretation
 facility

On 12/17/21 11:58 AM, Christian Borntraeger wrote:
> 
> 
> Am 17.12.21 um 16:19 schrieb Matthew Rosato:
>> On 12/17/21 10:05 AM, Christian Borntraeger wrote:
>>>
>>>
>>> Am 07.12.21 um 21:57 schrieb Matthew Rosato:
>>>> This facility will be used to enable interpretive execution of zPCI
>>>> instructions.
>>>>
>>>> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
>>>> ---
>>>>   arch/s390/kvm/kvm-s390.c | 4 ++++
>>>>   1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index c8fe9b7c2395..09991d05c871 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -2751,6 +2751,10 @@ int kvm_arch_init_vm(struct kvm *kvm, 
>>>> unsigned long type)
>>>>           set_kvm_facility(kvm->arch.model.fac_mask, 147);
>>>>           set_kvm_facility(kvm->arch.model.fac_list, 147);
>>>>       }
>>>> +    if (sclp.has_zpci_interp && test_facility(69)) {
>>>> +        set_kvm_facility(kvm->arch.model.fac_mask, 69);
>>>> +        set_kvm_facility(kvm->arch.model.fac_list, 69);
>>>> +    }
>>>
>>>
>>> Do we need the setting of these stfle bits somewhere? I think QEMU 
>>> sets them as well for the guest. > We only need this when the kernel 
>>> probes for this (test_kvm_facility)
>>> But then the question is, shouldnt
>>> we then simply check for sclp bits in those places?
>>> See also patch 19. We need to build it in a way that allows VSIE 
>>> support later on.
>>>
>>
>> Right, so this currently sets the facility bits but we don't set the 
>> associated guest SCLP bits.  I guess since we are not enabling for 
>> VSIE now it would make sense to not set either.
>>
>> So then just to confirm we are on the same page:  I will drop these 
>> patches 16-18 and leave the kvm facilities unset until we wish to 
>> enable VSIE.  And then also make sure we are checking sclp bits (e.g. 
>> patch 19).  OK?
> 
> Right drop these patches and change patch 19. When we later enable VSIE 
> we need QEMU to set the sclp bits. Not sure, does this work as of today 
> or do we need additional vsie changes (I would assume so)?

No, we will need some additional work to be able to enable for VSIE 
(e.g. adapter interrupt source ID)