KVM: x86/mmu: Extract zapping of rmaps for gfn range to separate helper

Extract the zapping of rmaps, a.k.a. legacy MMU, for a gfn range to a
separate helper to clean up the unholy mess that kvm_zap_gfn_range() has
become.  In addition to deep nesting, the rmaps zapping spreads out the
declaration of several variables and is generally a mess.  Clean up the
mess now so that future work to improve the memslots implementation
doesn't need to deal with it.

Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211022010005.1454978-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -5710,41 +5710,49 @@ void kvm_mmu_uninit_vm(struct kvm *kvm)
 	kvm_mmu_uninit_tdp_mmu(kvm);
 }
 
-/*
- * Invalidate (zap) SPTEs that cover GFNs from gfn_start and up to gfn_end
- * (not including it)
- */
-void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
+static bool __kvm_zap_rmaps(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 {
+	const struct kvm_memory_slot *memslot;
 	struct kvm_memslots *slots;
-	struct kvm_memory_slot *memslot;
-	int i;
 	bool flush = false;
+	gfn_t start, end;
+	int i;
 
-	write_lock(&kvm->mmu_lock);
-
-	kvm_inc_notifier_count(kvm, gfn_start, gfn_end);
+	if (!kvm_memslots_have_rmaps(kvm))
+		return flush;
 
-	if (kvm_memslots_have_rmaps(kvm)) {
 	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
 		slots = __kvm_memslots(kvm, i);
 		kvm_for_each_memslot(memslot, slots) {
-				gfn_t start, end;
-
 			start = max(gfn_start, memslot->base_gfn);
 			end = min(gfn_end, memslot->base_gfn + memslot->npages);
 			if (start >= end)
 				continue;
 
-				flush = slot_handle_level_range(kvm,
-						(const struct kvm_memory_slot *) memslot,
-						kvm_zap_rmapp, PG_LEVEL_4K,
-						KVM_MAX_HUGEPAGE_LEVEL, start,
-						end - 1, true, flush);
-			}
+			flush = slot_handle_level_range(kvm, memslot, kvm_zap_rmapp,
+							PG_LEVEL_4K, KVM_MAX_HUGEPAGE_LEVEL,
+							start, end - 1, true, flush);
 		}
 	}
 
+	return flush;
+}
+
+/*
+ * Invalidate (zap) SPTEs that cover GFNs from gfn_start and up to gfn_end
+ * (not including it)
+ */
+void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
+{
+	bool flush;
+	int i;
+
+	write_lock(&kvm->mmu_lock);
+
+	kvm_inc_notifier_count(kvm, gfn_start, gfn_end);
+
+	flush = __kvm_zap_rmaps(kvm, gfn_start, gfn_end);
+
 	if (is_tdp_mmu_enabled(kvm)) {
 		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++)
 			flush = kvm_tdp_mmu_zap_gfn_range(kvm, i, gfn_start,