Re: [PATCH v5 05/13] KVM: Integrate gfn_to_memslot_approx() into search_memslots()

[Maciej S. Szmigiero]

On 20.10.2021 01:38, Sean Christopherson wrote:
> On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote:
> > @@ -1267,7 +1280,7 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index)
> >    * itself isn't here as an inline because that would bloat other code too much.
> >    */
> >   static inline struct kvm_memory_slot *
> > -__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> > +__gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn, bool approx)
>
> This function name is a misnomer.  The helper is not an "approx" version, it's an
> inner helper that takes an @approx param.  Unless someone has a more clever name,
> the dreaded four underscores seems like the way to go.  Warning away users is a
> good thing in this case...
>
> >   {
> >   	struct kvm_memory_slot *slot;
> >   	int slot_index = atomic_read(&slots->last_used_slot);
> > @@ -1276,7 +1289,7 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> >   	if (slot)
> >   		return slot;
> >   
> > -	slot = search_memslots(slots, gfn, &slot_index);
> > +	slot = search_memslots(slots, gfn, &slot_index, approx);
> >   	if (slot) {
> >   		atomic_set(&slots->last_used_slot, slot_index);
> >   		return slot;
> > @@ -1285,6 +1298,12 @@ __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> >   	return NULL;
> >   }
> >   
>
> There's a comment that doesn't show up in this diff that should also be moved,
> and opportunistically updated.
>
> > +static inline struct kvm_memory_slot *
> > +__gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
> > +{
> > +	return __gfn_to_memslot_approx(slots, gfn, false);
> > +}
> > +
> >   static inline unsigned long
> >   __gfn_to_hva_memslot(const struct kvm_memory_slot *slot, gfn_t gfn)
> >   {
>
> E.g. this as fixup?
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 540fa948baa5..2964c773b36c 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1964,10 +1964,15 @@ static int kvm_s390_peek_cmma(struct kvm *kvm, struct kvm_s390_cmma_log *args,
>          return 0;
>   }
>
> +static int gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn)
> +{
> +       return ____gfn_to_memslot(slots, cur_gfn, true);
> +}
> +
>   static unsigned long kvm_s390_next_dirty_cmma(struct kvm_memslots *slots,
>                                                unsigned long cur_gfn)
>   {
> -       struct kvm_memory_slot *ms = __gfn_to_memslot_approx(slots, cur_gfn, true);
> +       struct kvm_memory_slot *ms = gfn_to_memslot_approx(slots, cur_gfn);
>          int slotidx = ms - slots->memslots;
>          unsigned long ofs = cur_gfn - ms->base_gfn;
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 8fd9644f40b2..ec1a074c2f6e 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1274,13 +1274,8 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn, int *index, bool approx)
>          return NULL;
>   }
>
> -/*
> - * __gfn_to_memslot() and its descendants are here because it is called from
> - * non-modular code in arch/powerpc/kvm/book3s_64_vio{,_hv}.c. gfn_to_memslot()
> - * itself isn't here as an inline because that would bloat other code too much.
> - */
>   static inline struct kvm_memory_slot *
> -__gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn, bool approx)
> +____gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn, bool approx)
>   {
>          struct kvm_memory_slot *slot;
>          int slot_index = atomic_read(&slots->last_used_slot);
> @@ -1298,10 +1293,15 @@ __gfn_to_memslot_approx(struct kvm_memslots *slots, gfn_t gfn, bool approx)
>          return NULL;
>   }
>
> +/*
> + * __gfn_to_memslot() and its descendants are here to allow arch code to inline
> + * the lookups in hot paths.  gfn_to_memslot() itself isn't here as an inline
> + * because that would bloat other code too much.
> + */
>   static inline struct kvm_memory_slot *
>   __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn)
>   {
> -       return __gfn_to_memslot_approx(slots, gfn, false);
> +       return ____gfn_to_memslot(slots, gfn, false);
>   }
>
>   static inline unsigned long

Looks sensible, will apply your proposed changes.

Thanks,
Maciej