linux-kernel - Re: [PATCH] KVM: x86: remove duplicated KVM_REQ

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Message-ID: <87h802g42r.fsf@vitty.brq.redhat.com>
Date:   Fri, 07 Feb 2020 10:05:32 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     "kvm\@vger.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86\@kernel.org" <x86@...nel.org>,
        "pbonzini\@redhat.com" <pbonzini@...hat.com>,
        "rkrcmar\@redhat.com" <rkrcmar@...hat.com>,
        "sean.j.christopherson\@intel.com" <sean.j.christopherson@...el.com>,
        "wanpengli\@tencent.com" <wanpengli@...cent.com>,
        "jmattson\@google.com" <jmattson@...gle.com>,
        "joro\@8bytes.org" <joro@...tes.org>,
        "tglx\@linutronix.de" <tglx@...utronix.de>,
        "mingo\@redhat.com" <mingo@...hat.com>,
        "bp\@alien8.de" <bp@...en8.de>, "hpa\@zytor.com" <hpa@...or.com>
Subject: Re: [PATCH] KVM: x86: remove duplicated KVM_REQ_EVENT request

linmiaohe <linmiaohe@...wei.com> writes:

> Hi：
> Vitaly Kuznetsov <vkuznets@...hat.com> writes:
>> linmiaohe <linmiaohe@...wei.com> writes:
>>> From: Miaohe Lin <linmiaohe@...wei.com>
>>>
>>> The KVM_REQ_EVENT request is already made in kvm_set_rflags(). We 
>>> should not make it again.
>>>  	kvm_rip_write(vcpu, ctxt->eip);
>>>  	kvm_set_rflags(vcpu, ctxt->eflags);
>>> -	kvm_make_request(KVM_REQ_EVENT, vcpu);
>>
>> I would've actually done it the other way around and removed
>> kvm_make_request() from kvm_set_rflags() as it is not an obvious behavior (e.g. why kvm_rip_write() doens't do that and kvm_set_rflags() does ?) adding kvm_make_request() to all call sites.
>>
>>In case this looks like too big of a change with no particular gain I'd suggest you at least leave a comment above kvm_set_rflags(), something like
>>
>>"kvm_make_request() also requests KVM_REQ_EVENT"
>
> I think adding kvm_make_request() to all call sites is too big without particular gain. And also leave a comment above
> kvm_set_rflags() maybe isn't needed as rflags updates is an site that can trigger event injection. Please see commit
> (3842d135ff24 KVM: Check for pending events before attempting injection) for detail.
>
> What do you think?

I don't have a strong opinion on this and your change is correct so feel
free to throw my

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>


-- 
Vitaly