Re: [PATCH v13 12/21] KVM: x86/xen: allow shared_info to be mapped by fixed HVA

[Paul Durrant]

On 19/02/2024 21:53, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
> > @@ -715,13 +731,23 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
> >   		break;
> >   
> >   	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
> > -		if (kvm->arch.xen.shinfo_cache.active)
> > +		if (kvm->arch.xen.shinfo_cache.active &&
> > +		    kvm->arch.xen.shinfo_cache.gpa != KVM_XEN_INVALID_GPA)
>
> This should really use INVALID_GPA when checking internal gpc state.  Mostly to
> help clarify what is/isn't KVM Xen ABI, but also because I don't like the subtle
> assumption that KVM_XEN_INVALID_GPA == INVALID_GPA.

Sorry, yes, that was miss on my part.

> Even better, if we slot in two helpers when the HVA-based GPC support is added,
> then the Xen code doesn't need to to make assumptions about how the GPC code
> manages HVA vs. GPA internally.  E.g. if we ever refactor the code again and use
> a dedicated flag instead of gpc->gpa as the implicit flag.
>
>    static inline bool kvm_gpc_is_gpa_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && !kvm_is_error_gpa(gpc->gpa);
>    }
>
>    static inline bool kvm_gpc_is_hva_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && kvm_is_error_gpa(gpc->gpa);
>    }

Sure, sounds good to me. I'll add those.