[PATCH v2 20/26] KVM: x86/mmu: Extend Eager Page Splitting to the shadow MMU

[David Matlack]

On Wed, Mar 30, 2022 at 11:34 AM Peter Xu <peterx at redhat.com> wrote:
>
> On Tue, Mar 22, 2022 at 04:58:08PM -0700, David Matlack wrote:
> > > > +static int prepare_to_split_huge_page(struct kvm *kvm,
> > > > +                                   const struct kvm_memory_slot *slot,
> > > > +                                   u64 *huge_sptep,
> > > > +                                   struct kvm_mmu_page **spp,
> > > > +                                   bool *flush,
> > > > +                                   bool *dropped_lock)
> > > > +{
> > > > +     int r = 0;
> > > > +
> > > > +     *dropped_lock = false;
> > > > +
> > > > +     if (kvm_mmu_available_pages(kvm) <= KVM_MIN_FREE_MMU_PAGES)
> > > > +             return -ENOSPC;
> > > > +
> > > > +     if (need_resched() || rwlock_needbreak(&kvm->mmu_lock))
> > > > +             goto drop_lock;
> > > > +
> > >
> > > Not immediately clear on whether there'll be case that *spp is set within
> > > the current function.  Some sanity check might be nice?
> >
> > Sorry I'm not sure what you mean here. What kind of sanity check did
> > you have in mind?
>
> Something like "WARN_ON_ONCE(*spp);"?

Ah I see. I was confused because the previous version of this code
checked if *spp is already set and, if so, skipped the allocation. But
I accidentally introduced a memory leak here when I implemented Ben'
suggestion to defer alloc_memory_for_split() to a subsequent commit.
I'll fix this in v3.

>
> >
> > >
> > > > +     *spp = kvm_mmu_alloc_direct_sp_for_split(true);
> > > > +     if (r)
> > > > +             goto drop_lock;
> > > > +
> > > > +     return 0;
>
> Thanks,
>
> --
> Peter Xu
>