KVM: MMU: reschedule during shadow teardown

Shadows for large guests can take a long time to tear down, so reschedule
occasionally to avoid softlockup warnings.
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/mmu.c

@@ -1858,6 +1858,7 @@ static void free_mmu_pages(struct kvm_vcpu *vcpu)
 		sp = container_of(vcpu->kvm->arch.active_mmu_pages.next,
 				  struct kvm_mmu_page, link);
 		kvm_mmu_zap_page(vcpu->kvm, sp);
+		cond_resched();
 	}
 	free_page((unsigned long)vcpu->arch.mmu.pae_root);
 }