x86/kvm/mmu: check if MMU reconfiguration is needed in init_kvm_nested_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>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 9ed046f..c73d9f6 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/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;