Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spteand mmu notifier to help KSM dirty bit tracking

[Izik Eidus]

On 6/22/2011 3:21 AM, Chris Wright wrote:
> * Nai Xia (nai.xia@xxxxxxxxx) wrote:
> > Introduced kvm_mmu_notifier_test_and_clear_dirty(), kvm_mmu_notifier_dirty_update()
> > and their mmu_notifier interfaces to support KSM dirty bit tracking, which brings
> > significant performance gain in volatile pages scanning in KSM.
> > Currently, kvm_mmu_notifier_dirty_update() returns 0 if and only if intel EPT is
> > enabled to indicate that the dirty bits of underlying sptes are not updated by
> > hardware.
> Did you test with each of EPT, NPT and shadow?
>
> > Signed-off-by: Nai Xia<nai.xia@xxxxxxxxx>
> > Acked-by: Izik Eidus<izik.eidus@xxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/kvm_host.h |    1 +
> >   arch/x86/kvm/mmu.c              |   36 +++++++++++++++++++++++++++++
> >   arch/x86/kvm/mmu.h              |    3 +-
> >   arch/x86/kvm/vmx.c              |    1 +
> >   include/linux/kvm_host.h        |    2 +-
> >   include/linux/mmu_notifier.h    |   48 +++++++++++++++++++++++++++++++++++++++
> >   mm/mmu_notifier.c               |   33 ++++++++++++++++++++++++++
> >   virt/kvm/kvm_main.c             |   27 ++++++++++++++++++++++
> >   8 files changed, 149 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index d2ac8e2..f0d7aa0 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -848,6 +848,7 @@ extern bool kvm_rebooting;
> >   int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
> >   int kvm_age_hva(struct kvm *kvm, unsigned long hva);
> >   int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
> > +int kvm_test_and_clear_dirty_hva(struct kvm *kvm, unsigned long hva);
> >   void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
> >   int cpuid_maxphyaddr(struct kvm_vcpu *vcpu);
> >   int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
> > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> > index aee3862..a5a0c51 100644
> > --- a/arch/x86/kvm/mmu.c
> > +++ b/arch/x86/kvm/mmu.c
> > @@ -979,6 +979,37 @@ out:
> >   	return young;
> >   }
> >
> > +/*
> > + * Caller is supposed to SetPageDirty(), it's not done inside this.
> > + */
> > +static
> > +int kvm_test_and_clear_dirty_rmapp(struct kvm *kvm, unsigned long *rmapp,
> > +				   unsigned long data)
> > +{
> > +	u64 *spte;
> > +	int dirty = 0;
> > +
> > +	if (!shadow_dirty_mask) {
> > +		WARN(1, "KVM: do NOT try to test dirty bit in EPT\n");
> > +		goto out;
> > +	}
> This should never fire with the dirty_update() notifier test, right?
> And that means that this whole optimization is for the shadow mmu case,
> arguably the legacy case.

Hi Chris,
AMD npt does track the dirty bit in the nested page tables,
so the shadow_dirty_mask should not be 0 in that case...
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