linux-kernel - Re: [PATCH v10 2/9] KVM: x86: Add & use kvm_vcpu_is_legal

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Message-ID: <ZL/y2CKoJ/bTOR0M@google.com>
Date:   Tue, 25 Jul 2023 09:05:44 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     Isaku Yamahata <isaku.yamahata@...il.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        chao.gao@...el.com, kai.huang@...el.com, David.Laight@...lab.com,
        robert.hu@...ux.intel.com, guang.zeng@...el.com
Subject: Re: [PATCH v10 2/9] KVM: x86: Add & use kvm_vcpu_is_legal_cr3() to
 check CR3's legality

On Mon, Jul 24, 2023, Binbin Wu wrote:
> 
> 
> On 7/21/2023 11:03 PM, Sean Christopherson wrote:
> > On Fri, Jul 21, 2023, Binbin Wu wrote:
> > > 
> > > On 7/21/2023 7:53 AM, Isaku Yamahata wrote:
> > > > On Wed, Jul 19, 2023 at 10:41:24PM +0800,
> > > > Binbin Wu <binbin.wu@...ux.intel.com> wrote:
> > > > 
> > > > > Add and use kvm_vcpu_is_legal_cr3() to check CR3's legality to provide
> > > > > a clear distinction b/t CR3 and GPA checks. So that kvm_vcpu_is_legal_cr3()
> > > > > can be adjusted according to new feature(s).
> > > > > 
> > > > > No functional change intended.
> > > > > 
> > > > > Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> > > > > ---
> > > > >    arch/x86/kvm/cpuid.h      | 5 +++++
> > > > >    arch/x86/kvm/svm/nested.c | 4 ++--
> > > > >    arch/x86/kvm/vmx/nested.c | 4 ++--
> > > > >    arch/x86/kvm/x86.c        | 4 ++--
> > > > >    4 files changed, 11 insertions(+), 6 deletions(-)
> > > > > 
> > > > > diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> > > > > index f61a2106ba90..8b26d946f3e3 100644
> > > > > --- a/arch/x86/kvm/cpuid.h
> > > > > +++ b/arch/x86/kvm/cpuid.h
> > > > > @@ -283,4 +283,9 @@ static __always_inline bool guest_can_use(struct kvm_vcpu *vcpu,
> > > > >    	return vcpu->arch.governed_features.enabled & kvm_governed_feature_bit(x86_feature);
> > > > >    }
> > > > > +static inline bool kvm_vcpu_is_legal_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
> > > > > +{
> > > > > +	return kvm_vcpu_is_legal_gpa(vcpu, cr3);
> > > > > +}
> > > > > +
> > > > The remaining user of kvm_vcpu_is_illegal_gpa() is one left.  Can we remove it
> > > > by replacing !kvm_vcpu_is_legal_gpa()?
> > > There are still two callsites of kvm_vcpu_is_illegal_gpa() left (basing on
> > > Linux 6.5-rc2), in handle_ept_violation() and nested_vmx_check_eptp().
> > > But they could be replaced by !kvm_vcpu_is_legal_gpa() and then remove
> > > kvm_vcpu_is_illegal_gpa().
> > > I am neutral to this.
> > I'm largely neutral on this as well, though I do like the idea of having only
> > "legal" APIs.  I think it makes sense to throw together a patch, we can always
> > ignore the patch if end we up deciding to keep kvm_vcpu_is_illegal_gpa().
> OK. Thanks for the advice.
> Should I send a seperate patch or add a patch to remove
> kvm_vcpu_is_illegal_gpa() in next version?

Add a patch in the next version, eliminating kvm_vcpu_is_illegal_gpa() without
the context of this series probably isn't worth the churn.