KVM: Move setting of memslot into helper routine

Split out the core functionality of setting a memslot into a separate
helper in preparation for moving memslot deletion into its own routine.

Tested-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -983,6 +983,66 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
 	return old_memslots;
 }
 
+static int kvm_set_memslot(struct kvm *kvm,
+			   const struct kvm_userspace_memory_region *mem,
+			   const struct kvm_memory_slot *old,
+			   struct kvm_memory_slot *new, int as_id,
+			   enum kvm_mr_change change)
+{
+	struct kvm_memory_slot *slot;
+	struct kvm_memslots *slots;
+	int r;
+
+	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
+	if (!slots)
+		return -ENOMEM;
+	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
+
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE) {
+		/*
+		 * Note, the INVALID flag needs to be in the appropriate entry
+		 * in the freshly allocated memslots, not in @old or @new.
+		 */
+		slot = id_to_memslot(slots, old->id);
+		slot->flags |= KVM_MEMSLOT_INVALID;
+
+		/*
+		 * We can re-use the old memslots, the only difference from the
+		 * newly installed memslots is the invalid flag, which will get
+		 * dropped by update_memslots anyway.  We'll also revert to the
+		 * old memslots if preparing the new memory region fails.
+		 */
+		slots = install_new_memslots(kvm, as_id, slots);
+
+		/* From this point no new shadow pages pointing to a deleted,
+		 * or moved, memslot will be created.
+		 *
+		 * validation of sp->gfn happens in:
+		 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
+		 *	- kvm_is_visible_gfn (mmu_check_root)
+		 */
+		kvm_arch_flush_shadow_memslot(kvm, slot);
+	}
+
+	r = kvm_arch_prepare_memory_region(kvm, new, mem, change);
+	if (r)
+		goto out_slots;
+
+	update_memslots(slots, new, change);
+	slots = install_new_memslots(kvm, as_id, slots);
+
+	kvm_arch_commit_memory_region(kvm, mem, old, new, change);
+
+	kvfree(slots);
+	return 0;
+
+out_slots:
+	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
+		slots = install_new_memslots(kvm, as_id, slots);
+	kvfree(slots);
+	return r;
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -999,7 +1059,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	unsigned long npages;
 	struct kvm_memory_slot *slot;
 	struct kvm_memory_slot old, new;
-	struct kvm_memslots *slots;
 	int as_id, id;
 	enum kvm_mr_change change;
 
@@ -1086,58 +1145,19 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			return r;
 	}
 
-	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
-	if (!slots) {
-		r = -ENOMEM;
-		goto out_bitmap;
-	}
-	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
-
-	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
-		slot = id_to_memslot(slots, id);
-		slot->flags |= KVM_MEMSLOT_INVALID;
-
-		/*
-		 * We can re-use the old memslots, the only difference from the
-		 * newly installed memslots is the invalid flag, which will get
-		 * dropped by update_memslots anyway.  We'll also revert to the
-		 * old memslots if preparing the new memory region fails.
-		 */
-		slots = install_new_memslots(kvm, as_id, slots);
-
-		/* From this point no new shadow pages pointing to a deleted,
-		 * or moved, memslot will be created.
-		 *
-		 * validation of sp->gfn happens in:
-		 *	- gfn_to_hva (kvm_read_guest, gfn_to_pfn)
-		 *	- kvm_is_visible_gfn (mmu_check_root)
-		 */
-		kvm_arch_flush_shadow_memslot(kvm, slot);
-	}
-
-	r = kvm_arch_prepare_memory_region(kvm, &new, mem, change);
-	if (r)
-		goto out_slots;
-
 	/* actual memory is freed via old in kvm_free_memslot below */
 	if (change == KVM_MR_DELETE) {
 		new.dirty_bitmap = NULL;
 		memset(&new.arch, 0, sizeof(new.arch));
 	}
 
-	update_memslots(slots, &new, change);
-	slots = install_new_memslots(kvm, as_id, slots);
-
-	kvm_arch_commit_memory_region(kvm, mem, &old, &new, change);
+	r = kvm_set_memslot(kvm, mem, &old, &new, as_id, change);
+	if (r)
+		goto out_bitmap;
 
 	kvm_free_memslot(kvm, &old, &new);
-	kvfree(slots);
 	return 0;
 
-out_slots:
-	if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
-		slots = install_new_memslots(kvm, as_id, slots);
-	kvfree(slots);
 out_bitmap:
 	if (new.dirty_bitmap && !old.dirty_bitmap)
 		kvm_destroy_dirty_bitmap(&new);