linux-kernel - Re: [PATCH mm-unstable v1 1/5] mm/kvm: add mmu_notifier_test_clear

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Date:   Thu, 23 Feb 2023 13:12:24 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Michael Larabel <michael@...haellarabel.com>,
        kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-mm@...gle.com
Subject: Re: [PATCH mm-unstable v1 1/5] mm/kvm: add mmu_notifier_test_clear_young()

On Thu, Feb 23, 2023, Yu Zhao wrote:
> On Thu, Feb 23, 2023 at 10:14 AM Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > On Thu, Feb 16, 2023, Yu Zhao wrote:
> > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > > index 9c60384b5ae0..1b465df4a93d 100644
> > > --- a/virt/kvm/kvm_main.c
> > > +++ b/virt/kvm/kvm_main.c
> > > @@ -875,6 +875,63 @@ static int kvm_mmu_notifier_clear_young(struct mmu_notifier *mn,
> > >       return kvm_handle_hva_range_no_flush(mn, start, end, kvm_age_gfn);
> > >  }
> > >
> > > +static bool kvm_test_clear_young(struct kvm *kvm, unsigned long start,
> > > +                              unsigned long end, unsigned long *bitmap)
> > > +{
> > > +     int i;
> > > +     int key;
> > > +     bool success = true;
> > > +
> > > +     trace_kvm_age_hva(start, end);
> > > +
> > > +     key = srcu_read_lock(&kvm->srcu);
> > > +
> > > +     for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> > > +             struct interval_tree_node *node;
> > > +             struct kvm_memslots *slots = __kvm_memslots(kvm, i);
> > > +
> > > +             kvm_for_each_memslot_in_hva_range(node, slots, start, end - 1) {
> > > +                     gfn_t lsb_gfn;
> > > +                     unsigned long hva_start, hva_end;
> > > +                     struct kvm_gfn_range range = {
> > > +                             .slot = container_of(node, struct kvm_memory_slot,
> > > +                                                  hva_node[slots->node_idx]),
> > > +                     };
> > > +
> > > +                     hva_start = max(start, range.slot->userspace_addr);
> > > +                     hva_end = min(end - 1, range.slot->userspace_addr +
> > > +                                            range.slot->npages * PAGE_SIZE - 1);
> > > +
> > > +                     range.start = hva_to_gfn_memslot(hva_start, range.slot);
> > > +                     range.end = hva_to_gfn_memslot(hva_end, range.slot) + 1;
> > > +
> > > +                     if (WARN_ON_ONCE(range.end <= range.start))
> > > +                             continue;
> >
> > Extend __kvm_handle_hva_range() instead of copy-pasting.  At a very quick glance,
> > I believe all that is needed is (minus sanity checks):
> 
> Yes, will do.
> 
> I do need to add one more parameter to kvm_gfn_range, because that's
> what the current kvm_arch_test_clear_young() needs, assuming that
> function is acceptable.
> 
> Also, just a side note, from MM's POV, the following in
> __kvm_handle_hva_range() seems to forget to handle end == 0, if that's
> possible?

It's handled by the WARN_ON_ONCE() at the very top:

static __always_inline int __kvm_handle_hva_range(struct kvm *kvm,
						  const struct kvm_hva_range *range)
{
	if (WARN_ON_ONCE(range->end <= range->start))
		return 0;


> 
>   hva_end = min(range->end, slot->userspace_addr + (slot->npages <<
> PAGE_SHIFT));