KVM: SVM: allow enabling/disabling NPT by reloading only the architecture module

If NPT is enabled after loading both KVM modules on AMD and it should be
disabled, both KVM modules must be reloaded. If only the architecture module is
reloaded the behavior is undefined. With this patch it is possible to disable
NPT only by reloading the kvm_amd module.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/mmu.c

@@ -1870,6 +1870,12 @@ void kvm_enable_tdp(void)
 }
 EXPORT_SYMBOL_GPL(kvm_enable_tdp);
 
+void kvm_disable_tdp(void)
+{
+	tdp_enabled = false;
+}
+EXPORT_SYMBOL_GPL(kvm_disable_tdp);
+
 static void free_mmu_pages(struct kvm_vcpu *vcpu)
 {
 	struct kvm_mmu_page *sp;

arch/x86/kvm/svm.c

@@ -453,7 +453,8 @@ static __init int svm_hardware_setup(void)
 	if (npt_enabled) {
 		printk(KERN_INFO "kvm: Nested Paging enabled\n");
 		kvm_enable_tdp();
-	}
+	} else
+		kvm_disable_tdp();
 
 	return 0;
 

include/asm-x86/kvm_host.h

@@ -556,6 +556,7 @@ int kvm_fix_hypercall(struct kvm_vcpu *vcpu);
 int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t gva, u32 error_code);
 
 void kvm_enable_tdp(void);
+void kvm_disable_tdp(void);
 
 int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3);
 int complete_pio(struct kvm_vcpu *vcpu);