KVM: nSVM: do not mark all VMCB02 fields dirty on nested vmexit

Since L1 and L2 now use different VMCBs, most of the fields remain the
same in VMCB02 from one L2 run to the next.  Since KVM itself is not
looking at VMCB12's clean field, for now not much can be optimized.
However, in the future we could avoid more copies if the VMCB12's SEG
and DT sections are clean.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -404,24 +404,32 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 	svm->vmcb->save.cs = vmcb12->save.cs;
 	svm->vmcb->save.ss = vmcb12->save.ss;
 	svm->vmcb->save.ds = vmcb12->save.ds;
+	svm->vmcb->save.cpl = vmcb12->save.cpl;
+	vmcb_mark_dirty(svm->vmcb, VMCB_SEG);
+
 	svm->vmcb->save.gdtr = vmcb12->save.gdtr;
 	svm->vmcb->save.idtr = vmcb12->save.idtr;
+	vmcb_mark_dirty(svm->vmcb, VMCB_DT);
+
 	kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
 	svm_set_efer(&svm->vcpu, vmcb12->save.efer);
 	svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
 	svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);
-	svm->vmcb->save.cr2 = svm->vcpu.arch.cr2 = vmcb12->save.cr2;
+
+	svm->vcpu.arch.cr2 = vmcb12->save.cr2;
 	kvm_rax_write(&svm->vcpu, vmcb12->save.rax);
 	kvm_rsp_write(&svm->vcpu, vmcb12->save.rsp);
 	kvm_rip_write(&svm->vcpu, vmcb12->save.rip);
 
 	/* In case we don't even reach vcpu_run, the fields are not updated */
+	svm->vmcb->save.cr2 = svm->vcpu.arch.cr2;
 	svm->vmcb->save.rax = vmcb12->save.rax;
 	svm->vmcb->save.rsp = vmcb12->save.rsp;
 	svm->vmcb->save.rip = vmcb12->save.rip;
+
 	svm->vmcb->save.dr7 = vmcb12->save.dr7 | DR7_FIXED_1;
 	svm->vcpu.arch.dr6  = vmcb12->save.dr6 | DR6_ACTIVE_LOW;
-	svm->vmcb->save.cpl = vmcb12->save.cpl;
+	vmcb_mark_dirty(svm->vmcb, VMCB_DR);
 }
 
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
@@ -474,11 +482,9 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 
 	/*
 	 * Merge guest and host intercepts - must be called with vcpu in
-	 * guest-mode to take affect here
+	 * guest-mode to take effect.
 	 */
 	recalc_intercepts(svm);
-
-	vmcb_mark_all_dirty(svm->vmcb);
 }
 
 int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb12_gpa,