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

From: Izik Eidus
Date: Wed Jun 22 2011 - 02:22:18 EST

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
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.
+ */
+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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