linux-kernel - Re: [PATCH] KVM: x86/mmu: fix an incorrect comment in kvm_mmu_new

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Message-ID: <Y4Uqrs7SBDCKISll@liuwe-devbox-debian-v2>
Date:   Mon, 28 Nov 2022 21:39:58 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Wei Liu <wei.liu@...nel.org>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86/mmu: fix an incorrect comment in kvm_mmu_new_pgd

On Mon, Nov 28, 2022 at 06:02:46PM +0000, Sean Christopherson wrote:
> On Sun, Nov 27, 2022, Wei Liu wrote:
> > There is no function named kvm_mmu_ensure_valid_pgd.
> 
> () when referecing functions, here and in the comment.
> 
> > Fix the comment and remove the pair of braces to conform to Linux kernel
> > coding style.
> > 
> > Signed-off-by: Wei Liu <wei.liu@...nel.org>
> > ---
> >  arch/x86/kvm/mmu/mmu.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index b6f96d47e596..361574124fbe 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4452,10 +4452,12 @@ void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd)
> >  	struct kvm_mmu *mmu = vcpu->arch.mmu;
> >  	union kvm_mmu_page_role new_role = mmu->root_role;
> >  
> > -	if (!fast_pgd_switch(vcpu->kvm, mmu, new_pgd, new_role)) {
> > -		/* kvm_mmu_ensure_valid_pgd will set up a new root.  */
> > +	/*
> > +	 * Return immediately if no usable root is found. A new root will be
> 
> s/is/was
> 
> And technically, it may not be a "new" root, e.g. if a different vCPU creates a
> usable root between now and kvm_mmu_reload().
> 
> > +	 * set up in vcpu_enter_guest prior to the next vmenter.
> 
> s/vmenter/VM-Enter
> 
> Pointing a reader at vcpu_enter_guest() isn't very helpful since that's a massive
> function; kvm_mmu_reload() is where the real magic happens.  I generally prefer to
> avoid referencing functions in comments unless doing so is absolutely "necessary"
> because such comments always seem to become stale, but in this case I think it's
> worthwhile.
> 
> 	/*
> 	 * Return immediately if no usable was found, kvm_mmu_reload() will
> 	 * establish a valid root prior to the next VM-Enter.
> 	 */
> 

Thanks for the feedback. v2 coming shortly.

Thanks,
Wei.