Re: [PATCH v2 01/25] KVM: x86/mmu: avoid indirect call for get_cr3

Sean Christopherson
2022-03-08T16:53:19Z

On Tue, Mar 08, 2022, Paolo Bonzini wrote:
> On 3/8/22 17:32, Sean Christopherson wrote:
> >
> > Aha! An idea that would provide line of sight to avoiding retpoline in all cases
> > once we use static_call() for nested_ops, which I really want to do... Drop the
> > mmu hook entirely and replace it with:
> >
> > static inline kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu)
> > {
> > if (!mmu_is_nested(vcpu))
> > return kvm_read_cr3(vcpu);
> > else
> > return kvm_x86_ops.nested_ops->get_guest_pgd(vcpu);
> > }
>
> Makes sense, but I think you mean
>
> static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu,
> struct kvm_mmu *mmu)
> {
> if (unlikely(vcpu == &vcpu->arch.guest_mmu))

Well, not that certainly :-)

if (mmu == &vcpu->arch.guest_mmu)

But you're right, we need to be able to do kvm_read_cr3() for the actual nested_mmu.

> return kvm_x86_ops.nested_ops->get_guest_pgd(vcpu);
> else
> return kvm_read_cr3(vcpu);
> }
>
> ?