On 6/22/2011 1:43 PM, Avi Kivity wrote:
On 06/21/2011 04:32 PM, Nai Xia 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.
Can you quantify the performance gains?
+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;
+ }
+
+ spte = rmap_next(kvm, rmapp, NULL);
+ while (spte) {
+ int _dirty;
+ u64 _spte = *spte;
+ BUG_ON(!(_spte& PT_PRESENT_MASK));
+ _dirty = _spte& PT_DIRTY_MASK;
+ if (_dirty) {
+ dirty = 1;
+ clear_bit(PT_DIRTY_SHIFT, (unsigned long *)spte);
+ }
Racy. Also, needs a tlb flush eventually.
Hi, one of the issues is that the whole point of this patch is not do
tlb flush eventually,
But I see your point, because other users will not expect such behavior,
so maybe there is need into a parameter
flush_tlb=?, or add another mmu notifier call?
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