KVM: x86: don't reset root in kvm_mmu_setup()

Here is the code path which shows kvm_mmu_setup() is invoked after
kvm_mmu_create(). Since kvm_mmu_setup() is only invoked in this code path,
this means the root_hpa and prev_roots are guaranteed to be invalid. And
it is not necessary to reset it again.

    kvm_vm_ioctl_create_vcpu()
        kvm_arch_vcpu_create()
            vmx_create_vcpu()
                kvm_vcpu_init()
                    kvm_arch_vcpu_init()
                        kvm_mmu_create()
        kvm_arch_vcpu_setup()
            kvm_mmu_setup()
                kvm_init_mmu()

This patch set reset_roots to false in kmv_mmu_setup().

Fixes: 50c28f21d045dde8c52548f8482d456b3f0956f5
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -5417,7 +5417,12 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu)
 {
 	MMU_WARN_ON(VALID_PAGE(vcpu->arch.mmu.root_hpa));
 
-	kvm_init_mmu(vcpu, true);
+	/*
+	 * kvm_mmu_setup() is called only on vCPU initialization.  
+	 * Therefore, no need to reset mmu roots as they are not yet
+	 * initialized.
+	 */
+	kvm_init_mmu(vcpu, false);
 }
 
 static void kvm_mmu_invalidate_zap_pages_in_memslot(struct kvm *kvm,