KVM: nSVM: fix few bugs in the vmcb02 caching logic

* Define and use an invalid GPA (all ones) for init value of last
  and current nested vmcb physical addresses.

* Reset the current vmcb12 gpa to the invalid value when leaving
  the nested mode, similar to what is done on nested vmexit.

* Reset	the last seen vmcb12 address when disabling the nested SVM,
  as it relies on vmcb02 fields which are freed at that point.

Fixes: 4995a368 ("KVM: SVM: Use a separate vmcb for the nested L2 guest")
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210503125446.1353307-3-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -113,6 +113,7 @@
 #define VALID_PAGE(x) ((x) != INVALID_PAGE)
 
 #define UNMAPPED_GVA (~(gpa_t)0)
+#define INVALID_GPA (~(gpa_t)0)
 
 /* KVM Hugepage definitions for x86 */
 #define KVM_MAX_HUGEPAGE_LEVEL	PG_LEVEL_1G

arch/x86/kvm/svm/nested.c

@@ -872,6 +872,15 @@ void svm_free_nested(struct vcpu_svm *svm)
 	__free_page(virt_to_page(svm->nested.vmcb02.ptr));
 	svm->nested.vmcb02.ptr = NULL;
 
+	/*
+	 * When last_vmcb12_gpa matches the current vmcb12 gpa,
+	 * some vmcb12 fields are not loaded if they are marked clean
+	 * in the vmcb12, since in this case they are up to date already.
+	 *
+	 * When the vmcb02 is freed, this optimization becomes invalid.
+	 */
+	svm->nested.last_vmcb12_gpa = INVALID_GPA;
+
 	svm->nested.initialized = false;
 }
 
@@ -884,6 +893,8 @@ void svm_leave_nested(struct vcpu_svm *svm)
 
 	if (is_guest_mode(vcpu)) {
 		svm->nested.nested_run_pending = 0;
+		svm->nested.vmcb12_gpa = INVALID_GPA;
+
 		leave_guest_mode(vcpu);
 
 		svm_switch_vmcb(svm, &svm->vmcb01);

arch/x86/kvm/svm/svm.c

@@ -1235,8 +1235,8 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	svm->current_vmcb->asid_generation = 0;
 	svm->asid = 0;
 
-	svm->nested.vmcb12_gpa = 0;
-	svm->nested.last_vmcb12_gpa = 0;
+	svm->nested.vmcb12_gpa = INVALID_GPA;
+	svm->nested.last_vmcb12_gpa = INVALID_GPA;
 	vcpu->arch.hflags = 0;
 
 	if (!kvm_pause_in_guest(vcpu->kvm)) {