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

[Tony Krowiak <akrowiak@linux.vnet.ibm.com>]

On 02/28/2018 06:58 AM, David Hildenbrand wrote:
> On 28.02.2018 12:40, Christian Borntraeger wrote:
>>
>> 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@de.ibm.com>
>>>> Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.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)
>>
> Interesting, so we (I :) ) didn't implement vSIE support back then
> because we never indicated the AP facility (sensed by executing the
> instruction) to the guest.
>
> So ECA_APIE can be used when we sense the AP facility. Thanks!
All true.
>