linux-kernel - Re: [PATCH v2 04/15] KVM: s390: CPU model support for AP virtualization

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Date:   Wed, 28 Feb 2018 12:40:48 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        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,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, fiuczy@...ux.vnet.ibm.com,
        buendgen@...ibm.com
Subject: Re: [PATCH v2 04/15] KVM: s390: CPU model support for AP
 virtualization



On 02/28/2018 10:48 AM, David Hildenbrand wrote:
> On 27.02.2018 15:28, Tony Krowiak wrote:
>> Introduces a new CPU model feature and two CPU model
>> facilities to support AP virtualization for KVM guests.
>>
>> CPU model feature:
>>
>> The KVM_S390_VM_CPU_FEAT_AP feature indicates that the
>> AP facilities are installed on the KVM guest. This
>> feature will be enabled by the kernel only if the AP
>> facilities are installed on the linux host. This feature
>> must be specifically turned on for the KVM guest from
>> userspace to allow guest access to AP devices installed
>> on the linux host.
>>
>> CPU model facilities:
>>
>> 1. AP Query Configuration Information (QCI) facility is installed.
>>
>>    This is indicated by setting facilities bit 12 for
>>    the guest. The kernel will not enable this facility
>>    for the guest if it is not set on the host. This facility
>>    must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
>>    feature is not installed.
>>
>> 2. AP Facilities Test facility (APFT) is installed.
>>
>>    This is indicated by setting facilities bit 15 for
>>    the guest. The kernel will not enable this facility for
>>    the guest if it is not set on the host. This facility
>>    must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
>>    feature is not installed.
>>
>> Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
>> Reviewed-by: Halil Pasic <pasic@...ux.vnet.ibm.com>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
>> ---
>>  arch/s390/include/uapi/asm/kvm.h |    1 +
>>  arch/s390/kvm/kvm-s390.c         |    4 ++++
>>  arch/s390/tools/gen_facilities.c |    2 ++
>>  3 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 4cdaa55..a580dec 100644
>> --- a/arch/s390/include/uapi/asm/kvm.h
>> +++ b/arch/s390/include/uapi/asm/kvm.h
>> @@ -130,6 +130,7 @@ struct kvm_s390_vm_cpu_machine {
>>  #define KVM_S390_VM_CPU_FEAT_PFMFI	11
>>  #define KVM_S390_VM_CPU_FEAT_SIGPIF	12
>>  #define KVM_S390_VM_CPU_FEAT_KSS	13
>> +#define KVM_S390_VM_CPU_FEAT_AP		14
>>  struct kvm_s390_vm_cpu_feat {
>>  	__u64 feat[16];
>>  };
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index de1e299..c68ca86 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -347,6 +347,10 @@ static void kvm_s390_cpu_feat_init(void)
>>  
>>  	if (MACHINE_HAS_ESOP)
>>  		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP);
>> +
>> +	if (ap_instructions_installed()) /* AP instructions installed on host */
>> +		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP);
> 
> Don't we have a SIE specific AP feature? So is it true, that once we
> have AP instructions, we are allowed to use them for SIE? Isn't there a
> "AP interpretation facility" or anything like that? (that unlocks ECA_APIE)

This seems to be coupled to the AP facility and there is no facility or scp bit.
AP is too old to have that (predates STFLE)