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

Harald Freudenberger
2018-08-09T08:34:26Z

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 */
>> }
>> },
>>
>