From: Pierre Morel <pmorel@linux.ibm.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cohuck@redhat.com>,
kvm@vger.kernel.org
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
frankja@linux.ibm.com, david@redhat.com, thuth@redhat.com,
imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com
Subject: Re: [PATCH v2 2/2] s390:kvm: Topology expose TOPOLOGY facility
Date: Fri, 23 Jul 2021 12:10:03 +0200 [thread overview]
Message-ID: <68c2e0d0-b591-7701-700c-400f1f040ca9@linux.ibm.com> (raw)
In-Reply-To: <46229585-507d-70a2-cc60-c06fb172fbfd@de.ibm.com>
On 7/23/21 11:28 AM, Christian Borntraeger wrote:
>
>
> On 23.07.21 10:55, Cornelia Huck wrote:
>> On Fri, Jul 23 2021, Christian Borntraeger <borntraeger@de.ibm.com>
>> wrote:
>>
>>> On 22.07.21 19:02, Pierre Morel wrote:
>>>> We add a KVM extension KVM_CAP_S390_CPU_TOPOLOGY to tell the
>>>> userland hypervisor it is safe to activate the CPU Topology facility.
>>>
>>> I think the old variant of using the CPU model was actually better.
>>> It was just the patch description that was wrong.
>>
>> I thought we wanted a cap that userspace can enable to get ptf
>> intercepts? I'm confused.
>>
>
> PTF goes to userspace in any case as every instruction that is
> not handled by kvm and where interpretion is not enabled.
> Now, having said that, we actually want PTF interpretion to be enabled
> for "Check topology-change status" as this is supposed to be a fast
> operation. Some OSes do query that in their interrupt handlers.
>
An old QEMU getting the PTF instruction will send a OPERATION exception
to the guest if the facility 11 is actzivated.
Facility 11 is in QEMU since GAEN10_GA1, if I enable the facility in the
CPU model all cpu model starting with GEN10_GA1 will panic on PTF.
So I think we need the capability so that new QEMU enable the facility
once it has the right handling for PTF.
>
>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>>> ---
>>>> arch/s390/kvm/kvm-s390.c | 1 +
>>>> include/uapi/linux/kvm.h | 1 +
>>>> 2 files changed, 2 insertions(+)
>>>>
>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>>>> index b655a7d82bf0..8c695ee79612 100644
>>>> --- a/arch/s390/kvm/kvm-s390.c
>>>> +++ b/arch/s390/kvm/kvm-s390.c
>>>> @@ -568,6 +568,7 @@ int kvm_vm_ioctl_check_extension(struct kvm
>>>> *kvm, long ext)
>>>> case KVM_CAP_S390_VCPU_RESETS:
>>>> case KVM_CAP_SET_GUEST_DEBUG:
>>>> case KVM_CAP_S390_DIAG318:
>>>> + case KVM_CAP_S390_CPU_TOPOLOGY:
>>>> r = 1;
>>>> break;
>>>> case KVM_CAP_SET_GUEST_DEBUG2:
>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>>> index d9e4aabcb31a..081ce0cd44b9 100644
>>>> --- a/include/uapi/linux/kvm.h
>>>> +++ b/include/uapi/linux/kvm.h
>>>> @@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
>>>> #define KVM_CAP_BINARY_STATS_FD 203
>>>> #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>>>> #define KVM_CAP_ARM_MTE 205
>>>> +#define KVM_CAP_S390_CPU_TOPOLOGY 206
>>>> #ifdef KVM_CAP_IRQ_ROUTING
>>>>
>>
>> Regardless of what we end up with: we need documentation for any new cap
>> :)
>>
--
Pierre Morel
IBM Lab Boeblingen
next prev parent reply other threads:[~2021-07-23 10:25 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-22 17:02 [PATCH v2 0/2] s390x: KVM: CPU Topology Pierre Morel
2021-07-22 17:02 ` [PATCH v2 1/2] s390x: KVM: accept STSI for CPU topology information Pierre Morel
2021-07-23 8:34 ` Christian Borntraeger
2021-07-22 17:02 ` [PATCH v2 2/2] s390:kvm: Topology expose TOPOLOGY facility Pierre Morel
2021-07-23 8:14 ` Christian Borntraeger
2021-07-23 8:55 ` Cornelia Huck
2021-07-23 9:28 ` Christian Borntraeger
2021-07-23 10:10 ` Pierre Morel [this message]
2021-07-23 10:24 ` Christian Borntraeger
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