Re: [PATCH v10 2/9] KVM: x86: Add & use kvm_vcpu_is_legal_cr3() to check CR3's legality

[Sean Christopherson <seanjc@google.com>]

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@linux.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@linux.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().