KVM: x86: switch kvm_set_memory_alias to SRCU update

Using a similar two-step procedure as for memslots.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 93bd307..20941c0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -266,6 +266,8 @@
 void kvm_disable_largepages(void);
 void kvm_arch_flush_shadow(struct kvm *kvm);
 gfn_t unalias_gfn(struct kvm *kvm, gfn_t gfn);
+gfn_t unalias_gfn_instantiation(struct kvm *kvm, gfn_t gfn);
+
 struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
 unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn);
 void kvm_release_page_clean(struct page *page);
@@ -539,6 +541,10 @@
 }
 #endif
 
+#ifndef KVM_ARCH_HAS_UNALIAS_INSTANTIATION
+#define unalias_gfn_instantiation unalias_gfn
+#endif
+
 #ifdef CONFIG_HAVE_KVM_IRQCHIP
 
 #define KVM_MAX_IRQ_ROUTES 1024