Re: [PATCH v8 21/22] KVM: s390: CPU model support for AP virtualization

[Harald Freudenberger <freude@linux.ibm.com>]

On 09.08.2018 10:17, David Hildenbrand wrote:
> On 08.08.2018 16:44, Tony Krowiak wrote:
>> From: Tony Krowiak <akrowiak@linux.ibm.com>
>>
>> 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
>> AP instructions are available on the guest. This
>> feature will be enabled by the kernel only if the AP
>> instructions are installed on the linux host. This feature
>> must be specifically turned on for the KVM guest from
>> userspace to use the VFIO AP device driver for guest
>> access to AP devices.
>>
>> 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.
> Could it happen on real HW (not frankenstein CPU models), that
>
> !AP, but STFL 12 or 15  are indicated?
What is your expectation here ? There are no AP instructions
available but if there would be AP instructions available then
there would be the QCI and or the T bit facility within
the PQAP AP instruction valid ?
>>    If this facility is not set for the KVM guest, then only
>>    APQNs with an APQI less than 16 will be used by a Linux
>>    guest regardless of the matrix configuration for the virtual
>>    machine. This is a limitation of the Linux AP bus.
>>
>> 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.
>>
>>    If this facility is not set for the KVM guest, then no
>>    AP devices will be available to the guest regardless of
>>    the guest's matrix configuration for the virtual
>>    machine. This is a limitation of the Linux AP bus.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
>> Tested-by: Michael Mueller <mimu@linux.ibm.com>
>> Tested-by: Farhan Ali <alifm@linux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>>  arch/s390/kvm/kvm-s390.c         |    7 +++++++
>>  arch/s390/tools/gen_facilities.c |    2 ++
>>  2 files changed, 9 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 9203f0b..7d4fe9b 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -367,6 +367,13 @@ static void kvm_s390_cpu_feat_init(void)
>>  
>>  	if (MACHINE_HAS_ESOP)
>>  		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_ESOP);
>> +
>> +	/*
>> +	 * Check if AP instructions installed on host
>> +	 */
> Make this a one-line comment, please.
>
>> +	if (ap_instructions_available() == 0)
>> +		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_AP);
>> +
>>  	/*
>>  	 * We need SIE support, ESOP (PROT_READ protection for gmap_shadow),
>>  	 * 64bit SCAO (SCA passthrough) and IDTE (for gmap_shadow unshadowing).
>> diff --git a/arch/s390/tools/gen_facilities.c b/arch/s390/tools/gen_facilities.c
>> index 90a8c9e..a52290b 100644
>> --- a/arch/s390/tools/gen_facilities.c
>> +++ b/arch/s390/tools/gen_facilities.c
>> @@ -106,6 +106,8 @@ struct facility_def {
>>  
>>  		.name = "FACILITIES_KVM_CPUMODEL",
>>  		.bits = (int[]){
>> +			12, /* AP Query Configuration Information */
>> +			15, /* AP Facilities Test */
>>  			-1  /* END */
>>  		}
>>  	},
>>
>