[RFC PATCH v11 05/29] KVM: Convert KVM_ARCH_WANT_MMU_NOTIFIER to CONFIG_KVM_GENERIC_MMU_NOTIFIER

[Yuan Yao]

On Wed, Jul 19, 2023 at 07:15:09AM -0700, Sean Christopherson wrote:
> On Wed, Jul 19, 2023, Yuan Yao wrote:
> > On Tue, Jul 18, 2023 at 04:44:48PM -0700, Sean Christopherson wrote:
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 90a0be261a5c..d2d3e083ec7f 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -255,7 +255,9 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> > >  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> > >  #endif
> > >
> > > -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> > > +struct kvm_gfn_range;
> >
> > Not sure why a declaration here, it's defined for ARCHs which defined
> > KVM_ARCH_WANT_MMU_NOTIFIER before.
>
> The forward declaration exists to handle cases where CONFIG_KVM=n, specifically
> arch/powerpc/include/asm/kvm_ppc.h's declaration of hooks to forward calls to
> uarch modules:
>
> 	bool (*unmap_gfn_range)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*test_age_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
> 	bool (*set_spte_gfn)(struct kvm *kvm, struct kvm_gfn_range *range);
>
> Prior to using a Kconfig, a forward declaration wasn't necessary because
> arch/powerpc/include/asm/kvm_host.h would #define KVM_ARCH_WANT_MMU_NOTIFIER even
> if CONFIG_KVM=n.
>
> Alternatively, kvm_ppc.h could declare the struct.  I went this route mainly to
> avoid the possibility of someone encountering the same problem on a different
> architecture.

Ah I see, thanks for your explanation!