linux-kernel - Re: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu

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Date:   Sun, 29 Aug 2021 08:25:10 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michael Mueller <mimu@...ux.ibm.com>
Subject: Re: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu_idx



On 27.08.21 23:23, Halil Pasic wrote:
> On Fri, 27 Aug 2021 18:36:48 +0200
> Christian Borntraeger <borntraeger@...ibm.com> wrote:
> 
>> On 27.08.21 16:06, Claudio Imbrenda wrote:
>>> On Fri, 27 Aug 2021 14:54:29 +0200
>>> Halil Pasic <pasic@...ux.ibm.com> wrote:
>>>    
>>>> While in practice vcpu->vcpu_idx ==  vcpu->vcp_id is often true,
> 
> s/vcp_id/vcpu_id/
> 
>>>> it may not always be, and we must not rely on this.
>>>
>>> why?
>>>
>>> maybe add a simple explanation of why vcpu_idx and vcpu_id can be
>>> different, namely:
>>> KVM decides the vcpu_idx, userspace decides the vcpu_id, thus the two
>>> might not match
>>>    
>>>>
>>>> Currently kvm->arch.idle_mask is indexed by vcpu_id, which implies
>>>> that code like
>>>> for_each_set_bit(vcpu_id, kvm->arch.idle_mask, online_vcpus) {
>>>>                   vcpu = kvm_get_vcpu(kvm, vcpu_id);
>>>
>>> you can also add a sentence to clarify that kvm_get_vcpu expects an
>>> vcpu_idx, not an vcpu_id.
>>>    
>>>> 		do_stuff(vcpu);
>>
>> I will modify the patch description accordingly before sending to Paolo.
>> Thanks for noticing.
> 
> Can you also please fix the typo I pointed out above (in the first line
> of the long description).

I already queued, but I think this is not a big deal.