x86/kvm/mmu: check if MMU reconfiguration is needed in init_kvm_neste…

…d_mmu()

We don't use root page role for nested_mmu, however, optimizing out
re-initialization in case nothing changed is still valuable as this
is done for every nested vmentry.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -4936,8 +4936,14 @@ static void init_kvm_softmmu(struct kvm_vcpu *vcpu)
 
 static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
 {
+ union kvm_mmu_role new_role = kvm_calc_mmu_role_common(vcpu, false);
  struct kvm_mmu *g_context = &vcpu->arch.nested_mmu;
 
+ new_role.base.word &= mmu_base_role_mask.word;
+ if (new_role.as_u64 == g_context->mmu_role.as_u64)
+ return;
+
+ g_context->mmu_role.as_u64 = new_role.as_u64;
  g_context->get_cr3 = get_cr3;
  g_context->get_pdptr = kvm_pdptr_read;
  g_context->inject_page_fault = kvm_inject_page_fault;