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Re: [qemu-s390x] [PATCH v8 2/6] s390x/cpumodel: Set up CPU model for AP

From: David Hildenbrand
Subject: Re: [qemu-s390x] [PATCH v8 2/6] s390x/cpumodel: Set up CPU model for AP device support
Date: Mon, 17 Sep 2018 10:21:22 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0

Am 17.09.18 um 10:19 schrieb David Hildenbrand:
> Am 12.09.18 um 22:08 schrieb Tony Krowiak:
>> A new CPU model feature and two new CPU model facilities are
>> introduced to support AP devices for a KVM guest.
>> CPU model features:
>> 1. The KVM_S390_VM_CPU_FEAT_AP CPU model feature indicates that
>>    AP facilities are installed. This feature will be enabled by
>>    the kernel only if the AP facilities are installed on the linux
>>    host. This feature must be turned on from userspace to access
>>    AP devices from the KVM guest. The QEMU command line to turn
>>    this feature looks something like this:
>>      qemu-system-s390x ... -cpu xxx,ap=on
>>    This feature will be supported for zEC12 and newer CPU models.
>>    The feature will not be supported for older models due to
>>    testability issues.
> I think we (me,  Halil and Pierre) agreed that this should not be a
> CPU_FEAT but instead some AP_INTERPRETATION toggle, that can be turned
> on/off dynamically. (CPU_FEAT cannot be changed after CPUs have been
> created).
> Can you discuss that with Halil + Pierre?

Just found patch #2, I don't see a reason for KVM_S390_VM_CPU_FEAT_AP
anymore. You can simply sense KVM_S390_VM_CRYPTO_ENABLE_APIE and use it
to indicate the AP cpu feature.



David / dhildenb

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