Re: [PATCH v7 21/22] KVM: s390: CPU model support for AP virtualization

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

On 07/31/2018 07:48 AM, Cornelia Huck wrote:
> On Thu, 26 Jul 2018 21:54:28 +0200
> Christian Borntraeger <borntraeger@de.ibm.com> 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.
>>
>>     If this facility is not set for the KVM guest, then only
>>     APQNs with an APQI less than 16 will be available to the
>>     guest regardless of the guest's matrix configuration. This
>>     is a limitation of the AP bus running on the guest.
> What is "the AP bus running on the guest"? The AP bus is a Linux
> construct, and while we only care about Linux guests right now for AP,
> I would not word it that way.
>
> "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."

You sure to write well for someone whose first language is not
English. I will substitute your edit as-is.

>
> ?
>
>> 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. This is a limitation
>>     of the AP bus running under the guest.
> Same here.

Ditto

>
>> 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(+)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 738b090fcf54..0eecc9ddb364 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
> /* check whether AP instructions are installed on host */
>
> ?
>
>> +	 */
>> +	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 90a8c9e84ca6..a52290bb8ad5 100644
>> --- a/arch/s390/tools/gen_facilities.c
>> +++ b/arch/s390/tools/gen_facilities.c
>> @@ -106,6 +106,8 @@ static struct facility_def facility_defs[] = {
>>   
>>   		.name = "FACILITIES_KVM_CPUMODEL",
>>   		.bits = (int[]){
>> +			12, /* AP Query Configuration Information */
>> +			15, /* AP Facilities Test */
>>   			-1  /* END */
>>   		}
>>   	},
> Other than the nits above, patch looks good to me.
>