linux-kernel - Re: [PATCH v8 1/2] s390x: KVM: guest support for topology function

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Message-ID: <f6c24447-2ed5-163a-8853-d70253eed0e8@linux.ibm.com>
Date:   Wed, 20 Apr 2022 20:31:22 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, cohuck@...hat.com, david@...hat.com,
        thuth@...hat.com, gor@...ux.ibm.com, wintera@...ux.ibm.com,
        seiden@...ux.ibm.com, nrb@...ux.ibm.com
Subject: Re: [PATCH v8 1/2] s390x: KVM: guest support for topology function



On 4/20/22 20:25, Heiko Carstens wrote:
> On Wed, Apr 20, 2022 at 03:22:41PM +0200, Claudio Imbrenda wrote:
>> On Wed, 20 Apr 2022 14:05:00 +0200
>> Heiko Carstens <hca@...ux.ibm.com> wrote:
>>
>>>> +static inline bool kvm_s390_topology_changed(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	if (!test_kvm_facility(vcpu->kvm, 11))
>>>> +		return false;
>>>> +
>>>> +	/* A new vCPU has been hotplugged */
>>>> +	if (vcpu->arch.prev_cpu == S390_KVM_TOPOLOGY_NEW_CPU)
>>>> +		return true;
>>>> +
>>>> +	/* The real CPU backing up the vCPU moved to another socket */
>>>> +	if (cpumask_test_cpu(vcpu->cpu,
>>>> +			     topology_core_cpumask(vcpu->arch.prev_cpu)))
>>>> +		return true;
>>>> +
>>>> +	return false;
>>>> +}
>>>
>>> This seems to be wrong. I'd guess that you need
>>>
>>> 	if (cpumask_test_cpu(vcpu->cpu,
>>> 			     topology_core_cpumask(vcpu->arch.prev_cpu)))
>>> -->		return false;
>>> -->	return true;
>>
>> so if the CPU moved to a different socket, it's not a change?
>> and if nothing happened, it is a change?
> 
> How do you translate the above code to your statement?
> 

Take care that the comment is also wrong.
I will of course change it too.

-- 
Pierre Morel
IBM Lab Boeblingen