On Mon, 24 Dec 2012 15:27:17 +0200
Gleb Natapov <g...@redhat.com> wrote:
> > @@ -6897,7 +6897,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> > spin_lock(&kvm->mmu_lock);
> > if (nr_mmu_pages)
> > kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
> > - kvm_mmu_slot_remove_write_access(kvm, mem->slot);
> > + /*
> > + * Write protect all pages for dirty logging.
> > + * Existing largepage mappings are destroyed here and new ones will
> > + * not be created until the end of the logging.
> > + */
> > + if ((mem->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
> > + !(old.flags & KVM_MEM_LOG_DIRTY_PAGES))
> > + kvm_mmu_slot_remove_write_access(kvm, mem->slot);
> We should not check old slot flags here or at least check that
> old.npages is not zero. Userspace may delete a slot using old flags,
> then, if new memslot is created with dirty log enabled, it will not be
> protected.
The flag, KVM_MEM_LOG_DIRTY_PAGES, is explicitely cleared when we
delete a slot to free dirty_bitmap:
if (!npages)
mem->flags &= ~KVM_MEM_LOG_DIRTY_PAGES;
So when old.npages is not zero, the second condition must be true.
Other parts are doing "if (!slot->dirty_bitmap)" to see if the slot
is in dirty logging mode. If you prefer, we can do the same here.
Thanks,
Takuya
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