KVM: Fix vcpu freeing for guest smp

A vcpu can pin up to four mmu shadow pages, which means the freeing
loop will never terminate.  Fix by first unpinning shadow pages on
all vcpus, then freeing shadow pages.
Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm_main.c

@@ -381,6 +381,16 @@ static void free_pio_guest_pages(struct kvm_vcpu *vcpu)
 		}
 }
 
+static void kvm_unload_vcpu_mmu(struct kvm_vcpu *vcpu)
+{
+	if (!vcpu->vmcs)
+		return;
+
+	vcpu_load(vcpu);
+	kvm_mmu_unload(vcpu);
+	vcpu_put(vcpu);
+}
+
 static void kvm_free_vcpu(struct kvm_vcpu *vcpu)
 {
 	if (!vcpu->vmcs)
@@ -401,6 +411,11 @@ static void kvm_free_vcpus(struct kvm *kvm)
 {
 	unsigned int i;
 
+	/*
+	 * Unpin any mmu pages first.
+	 */
+	for (i = 0; i < KVM_MAX_VCPUS; ++i)
+		kvm_unload_vcpu_mmu(&kvm->vcpus[i]);
 	for (i = 0; i < KVM_MAX_VCPUS; ++i)
 		kvm_free_vcpu(&kvm->vcpus[i]);
 }

drivers/kvm/mmu.c

@@ -838,11 +838,12 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 	int i;
 	struct kvm_mmu_page *page;
 
+	if (!VALID_PAGE(vcpu->mmu.root_hpa))
+		return;
 #ifdef CONFIG_X86_64
 	if (vcpu->mmu.shadow_root_level == PT64_ROOT_LEVEL) {
 		hpa_t root = vcpu->mmu.root_hpa;
 
-		ASSERT(VALID_PAGE(root));
 		page = page_header(root);
 		--page->root_count;
 		vcpu->mmu.root_hpa = INVALID_PAGE;
@@ -853,7 +854,6 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 		hpa_t root = vcpu->mmu.pae_root[i];
 
 		if (root) {
-			ASSERT(VALID_PAGE(root));
 			root &= PT64_BASE_ADDR_MASK;
 			page = page_header(root);
 			--page->root_count;