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SubjectRe: [PATCH v2 08/15] KVM: s390: interface to enable AP execution mode
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On 28.02.2018 21:39, Tony Krowiak wrote:
> On 02/28/2018 04:44 AM, David Hildenbrand wrote:
>> On 27.02.2018 15:28, Tony Krowiak wrote:
>>> Introduces a new interface to enable AP interpretive
>>> execution (IE) mode for the KVM guest. When running
>>> with IE mode enabled, AP instructions executed on the
>>> KVM guest will be interpreted by the firmware and
>>> passed directly through to an AP device installed on
>>> the system. The CPU model feature for AP must
>>> be enabled for the KVM guest in order to enable
>>> interpretive execution mode.
>>>
>>> This interface will be used in a subsequent patch
>>> by the VFIO AP device driver.
>>>
>>> Signed-off-by: Tony Krowiak <akrowiak@linux.vnet.ibm.com>
>>> ---
>>> arch/s390/include/asm/kvm-ap.h | 2 ++
>>> arch/s390/include/asm/kvm_host.h | 1 +
>>> arch/s390/kvm/kvm-ap.c | 27 +++++++++++++++++++++++++++
>>> arch/s390/kvm/kvm-s390.h | 1 +
>>> 4 files changed, 31 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/arch/s390/include/asm/kvm-ap.h b/arch/s390/include/asm/kvm-ap.h
>>> index 46e7c5b..6bd6bfb 100644
>>> --- a/arch/s390/include/asm/kvm-ap.h
>>> +++ b/arch/s390/include/asm/kvm-ap.h
>>> @@ -51,4 +51,6 @@ struct kvm_ap_matrix {
>>>
>>> void kvm_ap_deconfigure_matrix(struct kvm *kvm);
>>>
>>> +int kvm_ap_enable_ie_mode(struct kvm *kvm);
>>> +
>>> #endif /* _ASM_KVM_AP */
>>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>>> index a4c77d3..1eebdd6 100644
>>> --- a/arch/s390/include/asm/kvm_host.h
>>> +++ b/arch/s390/include/asm/kvm_host.h
>>> @@ -186,6 +186,7 @@ struct kvm_s390_sie_block {
>>> #define ECA_AIV 0x00200000
>>> #define ECA_VX 0x00020000
>>> #define ECA_PROTEXCI 0x00002000
>>> +#define ECA_APIE 0x00000008
>>> #define ECA_SII 0x00000001
>>> __u32 eca; /* 0x004c */
>>> #define ICPT_INST 0x04
>>> diff --git a/arch/s390/kvm/kvm-ap.c b/arch/s390/kvm/kvm-ap.c
>>> index bb29045..862e54b 100644
>>> --- a/arch/s390/kvm/kvm-ap.c
>>> +++ b/arch/s390/kvm/kvm-ap.c
>>> @@ -307,3 +307,30 @@ void kvm_ap_deconfigure_matrix(struct kvm *kvm)
>>> kvm_ap_clear_crycb_masks(kvm);
>>> }
>>> EXPORT_SYMBOL(kvm_ap_deconfigure_matrix);
>>> +
>>> +/**
>>> + * kvm_ap_enable_ie_mode
>>> + *
>>> + * Enable interpretrive execution of AP instructions for the guest. When
>>> + * enabled, AP instructions executed on the guest will be interpreted and
>>> + * passed through to an AP installed on the host system.
>>> + *
>>> + * Returns 0 if interpretrive execution is enabled. Returns -EOPNOTSUPP
>>> + * if AP facilities are not installed for the guest.
>>> + *
>>> + * @kvm: the guest's kvm structure
>>> + */
>>> +int kvm_ap_enable_ie_mode(struct kvm *kvm)
>>> +{
>>> + int i;
>>> + struct kvm_vcpu *vcpu;
>>> +
>>> + if (!test_kvm_cpu_feat(kvm, KVM_S390_VM_CPU_FEAT_AP))
>>> + return -EOPNOTSUPP;
>>> +
>>> + kvm_for_each_vcpu(i, vcpu, kvm)
>>> + vcpu->arch.sie_block->eca |= ECA_APIE;
>>> +
>>> + return 0;
>>> +}
>>> +EXPORT_SYMBOL(kvm_ap_enable_ie_mode);
>>> diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
>>> index 1b5621f..3142541 100644
>>> --- a/arch/s390/kvm/kvm-s390.h
>>> +++ b/arch/s390/kvm/kvm-s390.h
>>> @@ -18,6 +18,7 @@
>>> #include <asm/facility.h>
>>> #include <asm/processor.h>
>>> #include <asm/sclp.h>
>>> +#include <asm/ap.h>
>>>
>>> /* Transactional Memory Execution related macros */
>>> #define IS_TE_ENABLED(vcpu) ((vcpu->arch.sie_block->ecb & ECB_TE))
>>>
>> And also, what about hot-plugged CPUs?
> I haven't considered that, do you have any suggestions?

You should handle the KVM_S390_VM_CPU_FEAT_AP feature instead during
kvm_arch_vcpu_setup(), independent of any configured AP devices.

This avoids the races I mentioned in regards to this series and also
will handle hotplugged CPUs properly.

If KVM_S390_VM_CPU_FEAT_AP is configured for a guest -> each CPU sets
ECA_APIE during kvm_arch_vcpu_setup().


(In the vSIE code, simply allow to set ECA_APIE in the shadow SCB in
case KVM_S390_VM_CPU_FEAT_AP is enabled)

--

Thanks,

David / dhildenb

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