Re: [PATCH v12 08/20] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA

[Paul Durrant]

On 14/02/2024 16:01, Sean Christopherson wrote:
> On Tue, Feb 06, 2024, David Woodhouse wrote:
> > On Tue, 2024-02-06 at 20:03 -0800, Sean Christopherson wrote:
> > > +s390 folks (question on kvm_is_error_gpa() for ya)
> > >
> > > On Mon, Jan 15, 2024, Paul Durrant wrote:
> > > > @@ -1398,7 +1414,9 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
> > > >    static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
> > > >    {
> > > >          lockdep_assert_held(&gpc->lock);
> > > > -       mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
> > > > +
> > > > +       if (gpc->gpa != KVM_XEN_INVALID_GPA)
> > >
> > > KVM_XEN_INVALID_GPA absolutely doesn't belong in common code.  Not to mention
> > > that it will break when Paolo (rightly) moves it to an x86 header.
> > >
> > > https://lore.kernel.org/all/20240131233056.10845-3-pbonzini@xxxxxxxxxx
> >
> > We can use plain INVALID_GPA for that, I think. ISTR the reason we have
> > a separate KVM_XEN_INVALID_GPA is because that's a userspace API.
> >
> > ...
> >
> > > But!  kvm_is_error_gpa() already exists, and it very, very sneakily
> > > does a memslot lookup and checks for a valid HVA.
> >
> > Hm, that doesn't sound as fast as simple comparison. We also can't do
> > it from kvm_gpc_check(), can we?
>
> You snipped the part where I suggested renaming the existing kvm_is_error_gpa().
>
> I am suggesting we do the below (and obviously rename the s390 usage, too), and
> then the gpc code can use use kvm_is_error_gpa().
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index bbfefd7e612f..e1df988e4d57 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -148,6 +148,11 @@ static inline bool kvm_is_error_hva(unsigned long addr)
>   
>   #endif
>   
> +static inline bool kvm_is_error_gpa(gpa_t gpa)
> +{
> +       return gpa == INVALID_GPA;
> +}
> +

Are you ok with a local kvm_gpc_is_error_gpa() or somesuch until there 
is agreement with s390?

  Paul

>   #define KVM_ERR_PTR_BAD_PAGE   (ERR_PTR(-ENOENT))
>   
>   static inline bool is_error_page(struct page *page)
> @@ -1787,7 +1792,7 @@ static inline hpa_t pfn_to_hpa(kvm_pfn_t pfn)
>          return (hpa_t)pfn << PAGE_SHIFT;
>   }
>   
> -static inline bool kvm_is_error_gpa(struct kvm *kvm, gpa_t gpa)
> +static inline bool kvm_gpa_is_in_memslot(struct kvm *kvm, gpa_t gpa)
>   {
>          unsigned long hva = gfn_to_hva(kvm, gpa_to_gfn(gpa));
>