Re: [PATCH v4 3/7] KVM: Add lockless memslot walk to KVM

[James Houghton]

On Wed, May 29, 2024 at 2:51 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> On Wed, May 29, 2024, James Houghton wrote:
> > @@ -686,10 +694,12 @@ static __always_inline int kvm_handle_hva_range(struct mmu_notifier *mn,
> >       return __kvm_handle_hva_range(kvm, &range).ret;
> >  }
> >
> > -static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn,
> > -                                                      unsigned long start,
> > -                                                      unsigned long end,
> > -                                                      gfn_handler_t handler)
> > +static __always_inline int kvm_handle_hva_range_no_flush(
> > +             struct mmu_notifier *mn,
> > +             unsigned long start,
> > +             unsigned long end,
> > +             gfn_handler_t handler,
> > +             bool lockless)
>
> Unnecessary and unwanted style change.

Sorry -- this will be fixed.

>
> >  {
> >       struct kvm *kvm = mmu_notifier_to_kvm(mn);
> >       const struct kvm_mmu_notifier_range range = {
> > @@ -699,6 +709,7 @@ static __always_inline int kvm_handle_hva_range_no_flush(struct mmu_notifier *mn
> >               .on_lock        = (void *)kvm_null_fn,
> >               .flush_on_ret   = false,
> >               .may_block      = false,
> > +             .lockless       = lockless,
>
> Why add @lockess to kvm_handle_hva_range_no_flush()?  Both callers immediately
> pass %false, and conceptually, locking is always optional for a "no flush" variant.

Right, this isn't needed in this patch. But I think I need it
eventually (like, in the next patch), so I'll move it where it is
really needed.



>
> >       };
> >
> >       return __kvm_handle_hva_range(kvm, &range).ret;
> > @@ -889,7 +900,8 @@ static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
> >        * cadence. If we find this inaccurate, we might come up with a
> >        * more sophisticated heuristic later.
> >        */
> > -     return kvm_handle_hva_range_no_flush(mn, start, end, kvm_age_gfn);
> > +     return kvm_handle_hva_range_no_flush(mn, start, end,
> > +                                          kvm_age_gfn, false);
> >  }
> >
> >  static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
> > @@ -899,7 +911,7 @@ static int kvm_mmu_notifier_test_young(struct mmu_notifier *mn,
> >       trace_kvm_test_age_hva(address);
> >
> >       return kvm_handle_hva_range_no_flush(mn, address, address + 1,
> > -                                          kvm_test_age_gfn);
> > +                                          kvm_test_age_gfn, false);
> >  }
> >
> >  static void kvm_mmu_notifier_release(struct mmu_notifier *mn,
> > --
> > 2.45.1.288.g0e0cd299f1-goog
> >