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    SubjectRe: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking
    On 6/22/2011 3:21 AM, Chris Wright wrote:
    > * Nai Xia (nai.xia@gmail.com) 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@gmail.com>
    >> Acked-by: Izik Eidus<izik.eidus@ravellosystems.com>
    >> ---
    >> 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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