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

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Date:   Fri, 27 Aug 2021 23:23:44 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...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,
        stable@...r.kernel.org, Michael Mueller <mimu@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH 1/1] KVM: s390: index kvm->arch.idle_mask by vcpu_idx

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).

Thanks!
Halil