Commit 39214915 authored Jul 31, 2007 by Rusty Russell Committed by Avi Kivity Oct 13, 2007

KVM: kvm_vm_ioctl_get_dirty_log restore "nothing dirty" optimization



kvm_vm_ioctl_get_dirty_log scans bitmap to see it it's all zero, but
doesn't use that information.

Avi says:
	Looks like it was used to guard	kvm_mmu_slot_remove_write_access();
	optimizing the case where the guest just leaves the screen alone (which
	it usually does, especially in benchmarks).

	I'd rather reinstate that optimization.  See
	90cb0529 where the damage was done.

It's pretty simple: if the bitmap is all zero, we don't need to do anything to
clean it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>

parent b114b080

drivers/kvm/kvm_main.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -803,11 +803,14 @@ static int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
		if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
		goto out;

		/* If nothing is dirty, don't bother messing with page tables. */
		if (any) {
		mutex_lock(&kvm->lock);
		kvm_mmu_slot_remove_write_access(kvm, log->slot);
		kvm_flush_remote_tlbs(kvm);
		memset(memslot->dirty_bitmap, 0, n);
		mutex_unlock(&kvm->lock);
		}

		r = 0;

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