linux-kernel - Re: [PATCH v2 09/46] KVM: SVM: Drop a redundant init_vmcb() from svm_create

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Message-ID: <YP82lPKKy3hLv1de@google.com>
Date:   Mon, 26 Jul 2021 22:26:28 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Reiji Watanabe <reijiw@...gle.com>
Subject: Re: [PATCH v2 09/46] KVM: SVM: Drop a redundant init_vmcb() from
 svm_create_vcpu()

On Mon, Jul 26, 2021, Paolo Bonzini wrote:
> On 13/07/21 18:32, Sean Christopherson wrote:
> > Drop an extra init_vmcb() from svm_create_vcpu(), svm_vcpu_reset() is
> > guaranteed to call init_vmcb() and there are no consumers of the VMCB
> > data between ->vcpu_create() and ->vcpu_reset().  Keep the call to
> > svm_switch_vmcb() as sev_es_create_vcpu() touches the current VMCB, but
> > hoist it up a few lines to associate the switch with the allocation of
> > vmcb01.
> > 
> > Reviewed-by: Reiji Watanabe <reijiw@...gle.com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >   arch/x86/kvm/svm/svm.c | 4 +---
> >   1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 44248548be7d..cef9520fe77f 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -1431,15 +1431,13 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
> >   	svm->vmcb01.ptr = page_address(vmcb01_page);
> >   	svm->vmcb01.pa = __sme_set(page_to_pfn(vmcb01_page) << PAGE_SHIFT);
> > +	svm_switch_vmcb(svm, &svm->vmcb01);
> >   	if (vmsa_page)
> >   		svm->vmsa = page_address(vmsa_page);
> >   	svm->guest_state_loaded = false;
> > -	svm_switch_vmcb(svm, &svm->vmcb01);
> > -	init_vmcb(vcpu);
> > -
> >   	svm_init_osvw(vcpu);
> >   	vcpu->arch.microcode_version = 0x01000065;
> 
> While this patch makes sense, I'd rather not include it to reduce the part
> of the code in which svm->vmcb is NULL.

Not sure I follow.  The svm_switch_vmcb() is kept, and even moved earlier.