linux-kernel - Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm

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Date:   Thu, 23 Apr 2020 12:39:01 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        pbonzini@...hat.com, tsbogend@...ha.franken.de, paulus@...abs.org,
        mpe@...erman.id.au, benh@...nel.crashing.org,
        frankja@...ux.ibm.com, david@...hat.com, heiko.carstens@...ibm.com,
        gor@...ux.ibm.com, sean.j.christopherson@...el.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org, hpa@...or.com, maz@...nel.org,
        james.morse@....com, julien.thierry.kdev@...il.com,
        suzuki.poulose@....com, christoffer.dall@....com,
        peterx@...hat.com, thuth@...hat.com, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/7] KVM: s390: clean up redundant 'kvm_run'
 parameters

On Thu, 23 Apr 2020 11:01:43 +0800
Tianjia Zhang <tianjia.zhang@...ux.alibaba.com> wrote:

> On 2020/4/23 0:04, Cornelia Huck wrote:
> > On Wed, 22 Apr 2020 17:58:04 +0200
> > Christian Borntraeger <borntraeger@...ibm.com> wrote:
> >   
> >> On 22.04.20 15:45, Cornelia Huck wrote:  
> >>> On Wed, 22 Apr 2020 20:58:04 +0800
> >>> Tianjia Zhang <tianjia.zhang@...ux.alibaba.com> wrote:
> >>>      
> >>>> In the current kvm version, 'kvm_run' has been included in the 'kvm_vcpu'
> >>>> structure. Earlier than historical reasons, many kvm-related function  
> >>>
> >>> s/Earlier than/For/ ?
> >>>      
> >>>> parameters retain the 'kvm_run' and 'kvm_vcpu' parameters at the same time.
> >>>> This patch does a unified cleanup of these remaining redundant parameters.
> >>>>
> >>>> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> >>>> ---
> >>>>   arch/s390/kvm/kvm-s390.c | 37 ++++++++++++++++++++++---------------
> >>>>   1 file changed, 22 insertions(+), 15 deletions(-)
> >>>>
> >>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> >>>> index e335a7e5ead7..d7bb2e7a07ff 100644
> >>>> --- a/arch/s390/kvm/kvm-s390.c
> >>>> +++ b/arch/s390/kvm/kvm-s390.c
> >>>> @@ -4176,8 +4176,9 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
> >>>>   	return rc;
> >>>>   }
> >>>>   
> >>>> -static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> >>>> +static void sync_regs_fmt2(struct kvm_vcpu *vcpu)
> >>>>   {
> >>>> +	struct kvm_run *kvm_run = vcpu->run;
> >>>>   	struct runtime_instr_cb *riccb;
> >>>>   	struct gs_cb *gscb;
> >>>>   
> >>>> @@ -4235,7 +4236,7 @@ static void sync_regs_fmt2(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
> >>>>   		}
> >>>>   		if (vcpu->arch.gs_enabled) {
> >>>>   			current->thread.gs_cb = (struct gs_cb *)
> >>>> -						&vcpu->run->s.regs.gscb;
> >>>> +						&kvm_run->s.regs.gscb;  
> >>>
> >>> Not sure if these changes (vcpu->run-> => kvm_run->) are really worth
> >>> it. (It seems they amount to at least as much as the changes advertised
> >>> in the patch description.)
> >>>
> >>> Other opinions?  
> >>
> >> Agreed. It feels kind of random. Maybe just do the first line (move kvm_run from the
> >> function parameter list into the variable declaration)? Not sure if this is better.
> >>  
> > 
> > There's more in this patch that I cut... but I think just moving
> > kvm_run from the parameter list would be much less disruptive.
> >   
> 
> I think there are two kinds of code(`vcpu->run->` and `kvm_run->`), but 
> there will be more disruptive, not less.

I just fail to see the benefit; sure, kvm_run-> is convenient, but the
current code is just fine, and any rework should be balanced against
the cost (e.g. cluttering git annotate).