KVM: nVMX: always update CR3 in VMCS

vmx_load_mmu_pgd is delaying the write of GUEST_CR3 to prepare_vmcs02 as
an optimization, but this is only correct before the nested vmentry.
If userspace is modifying CR3 with KVM_SET_SREGS after the VM has
already been put in guest mode, the value of CR3 will not be updated.
Remove the optimization, which almost never triggers anyway.

Fixes: 04f11ef4 ("KVM: nVMX: Always write vmcs02.GUEST_CR3 during nested VM-Enter")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -3085,10 +3085,7 @@ void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long pgd)
 			spin_unlock(&to_kvm_vmx(kvm)->ept_pointer_lock);
 		}
 
-		/* Loading vmcs02.GUEST_CR3 is handled by nested VM-Enter. */
-		if (is_guest_mode(vcpu))
-			update_guest_cr3 = false;
-		else if (!enable_unrestricted_guest && !is_paging(vcpu))
+		if (!enable_unrestricted_guest && !is_paging(vcpu))
 			guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
 		else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
 			guest_cr3 = vcpu->arch.cr3;