Messages in this thread |  | | Date | Tue, 25 Dec 2012 13:08:40 +0900 | From | Takuya Yoshikawa <> | Subject | Re: [PATCH 1/7] KVM: Write protect the updated slot only when we start dirty logging |
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On Mon, 24 Dec 2012 15:27:17 +0200 Gleb Natapov <gleb@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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