linux-kernel - Re: [PATCH v2 08/15] KVM: s390: interface to enable AP execution mode

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Message-ID: <dd63866f-cf54-a11f-8bfd-cc2f9dbae9b7@redhat.com>
Date:   Thu, 1 Mar 2018 10:35:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, pmorel@...ux.vnet.ibm.com,
        alifm@...ux.vnet.ibm.com, mjrosato@...ux.vnet.ibm.com,
        jjherne@...ux.vnet.ibm.com, thuth@...hat.com,
        pasic@...ux.vnet.ibm.com, fiuczy@...ux.vnet.ibm.com,
        buendgen@...ibm.com
Subject: Re: [PATCH v2 08/15] KVM: s390: interface to enable AP execution mode

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@...ux.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