On Wednesday 22 June 2011 14:15:51 Izik Eidus wrote:

On 6/22/2011 3:21 AM, Chris Wright wrote:

quoted

* Nai Xia (nai.xia@gmail.com) wrote:

quoted

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?

quoted

Signed-off-by: Nai Xia<redacted>
Acked-by: Izik Eidus<redacted>
---
  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...

Hi Izik, 
I think he meant that if the caller is doing right && (!shadow_dirty_mask), 
the kvm_test_and_clear_dirty_rmapp() will never be called at all. So 
this test inside kvm_test_and_clear_dirty_rmapp() is useless...as I said
I added this test in any case of this interface abused by others, just like
a softer BUG_ON() --- dirty bit is not that critical to bump into BUG().



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