KVM: MMU: Avoid page prefetch on SVM

SVM cannot benefit from page prefetching since guest page fault bypass
cannot by made to work there.  Avoid accessing the guest page table in
this case.
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/mmu.c

@@ -850,7 +850,10 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	hlist_add_head(&sp->hash_link, bucket);
 	if (!metaphysical)
 		rmap_write_protect(vcpu->kvm, gfn);
-	vcpu->arch.mmu.prefetch_page(vcpu, sp);
+	if (shadow_trap_nonpresent_pte != shadow_notrap_nonpresent_pte)
+		vcpu->arch.mmu.prefetch_page(vcpu, sp);
+	else
+		nonpaging_prefetch_page(vcpu, sp);
 	return sp;
 }