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KVM: Write protect the updated slot only when dirty logging is enabled 

Calling kvm_mmu_slot_remove_write_access() for a deleted slot does
nothing but search for non-existent mmu pages which have mappings to
that deleted memory; this is safe but a waste of time.

Since we want to make the function rmap based in a later patch, in a
manner which makes it unsafe to be called for a deleted slot, we makes
the caller see if the slot is non-zero and being dirty logged.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
This commit is contained in:
Takuya Yoshikawa 2013-01-08 19:43:28 +09:00 committed by Gleb Natapov
parent aa11e3a8a6
commit c972f3b125
2 changed files with 7 additions and 2 deletions
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8
arch/x86/kvm/x86.c
View File

@ -6897,7 +6897,13 @@ 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 (npages && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
kvm_mmu_slot_remove_write_access(kvm, mem->slot);
spin_unlock(&kvm->mmu_lock);
/*
* If memory slot is created, or moved, we need to clear all

1
virt/kvm/kvm_main.c
View File

@ -817,7 +817,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
if (kvm_create_dirty_bitmap(&new) < 0)
goto out_free;
/* destroy any largepage mappings for dirty tracking */
}
if (!npages || base_gfn != old.base_gfn) {