linux-kernel - Re: Re: [PATCH 8/9] KVM: s390: Do not report unusabled IDs via KVM_CAP_MAX_VCPU

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Date:   Tue, 28 May 2019 15:48:57 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Huth <thuth@...hat.com>, kvm@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re:  Re: [PATCH 8/9] KVM: s390: Do not report unusabled IDs via
 KVM_CAP_MAX_VCPU_ID



On 28.05.19 14:53, Cornelia Huck wrote:
> On Tue, 28 May 2019 13:00:30 +0200
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> Paolo, Radim,
>>
>> would you consider this patch (or the full series) as 5.2 material or 5.3 material?
> 
> FWIW, I'd consider this patch 5.2 material, as we're currently relaying
> wrong values to userspace.

Agreed. I will add cc stable and queue for master. What is our opinion about kselftest?
Are we merging testtools changes also only during the merge window?
> 
>>
>>
>> On 23.05.19 18:43, Thomas Huth wrote:
>>> KVM_CAP_MAX_VCPU_ID is currently always reporting KVM_MAX_VCPU_ID on all
>>> architectures. However, on s390x, the amount of usable CPUs is determined
>>> during runtime - it is depending on the features of the machine the code
>>> is running on. Since we are using the vcpu_id as an index into the SCA
>>> structures that are defined by the hardware (see e.g. the sca_add_vcpu()
>>> function), it is not only the amount of CPUs that is limited by the hard-
>>> ware, but also the range of IDs that we can use.
>>> Thus KVM_CAP_MAX_VCPU_ID must be determined during runtime on s390x, too.
>>> So the handling of KVM_CAP_MAX_VCPU_ID has to be moved from the common
>>> code into the architecture specific code, and on s390x we have to return
>>> the same value here as for KVM_CAP_MAX_VCPUS.
>>> This problem has been discovered with the kvm_create_max_vcpus selftest.
>>> With this change applied, the selftest now passes on s390x, too.
>>>
>>> Signed-off-by: Thomas Huth <thuth@...hat.com>
>>> ---
>>>  arch/mips/kvm/mips.c       | 3 +++
>>>  arch/powerpc/kvm/powerpc.c | 3 +++
>>>  arch/s390/kvm/kvm-s390.c   | 1 +
>>>  arch/x86/kvm/x86.c         | 3 +++
>>>  virt/kvm/arm/arm.c         | 3 +++
>>>  virt/kvm/kvm_main.c        | 2 --
>>>  6 files changed, 13 insertions(+), 2 deletions(-)
>