diff --git a/nova/api/openstack/placement/exception.py b/nova/api/openstack/placement/exception.py
index d5a4461ef106..ae17d5470f67 100644
--- a/nova/api/openstack/placement/exception.py
+++ b/nova/api/openstack/placement/exception.py
@@ -99,6 +99,12 @@ class InvalidInventoryCapacity(InvalidInventory):
                 "The reserved value is greater than or equal to total.")
 
 
+class InvalidInventoryCapacityReservedCanBeTotal(InvalidInventoryCapacity):
+    msg_fmt = _("Invalid inventory for '%(resource_class)s' on "
+                "resource provider '%(resource_provider)s'. "
+                "The reserved value is greater than total.")
+
+
 # An exception with this name is used on both sides of the placement/
 # nova interaction.
 class InventoryInUse(InvalidInventory):
diff --git a/nova/api/openstack/placement/handlers/inventory.py b/nova/api/openstack/placement/handlers/inventory.py
index 3fed8ac42ca6..4e6aea60b8bd 100644
--- a/nova/api/openstack/placement/handlers/inventory.py
+++ b/nova/api/openstack/placement/handlers/inventory.py
@@ -12,6 +12,7 @@
 """Inventory handlers for Placement API."""
 
 import copy
+import operator
 
 from oslo_db import exception as db_exc
 from oslo_serialization import jsonutils
@@ -147,6 +148,31 @@ def _serialize_inventories(inventories, generation):
              'inventories': inventories_dict}, last_modified)
 
 
+def _validate_inventory_capacity(version, inventories):
+    """Validate inventory capacity.
+
+    :param version: request microversion.
+    :param inventories: Inventory or InventoryList to validate capacities of.
+    :raises: exception.InvalidInventoryCapacityReservedCanBeTotal if request
+        microversion is 1.26 or higher and any inventory has capacity < 0.
+    :raises: exception.InvalidInventoryCapacity if request
+        microversion is lower than 1.26 and any inventory has capacity <= 0.
+    """
+    if not version.matches((1, 26)):
+        op = operator.le
+        exc_class = exception.InvalidInventoryCapacity
+    else:
+        op = operator.lt
+        exc_class = exception.InvalidInventoryCapacityReservedCanBeTotal
+    if isinstance(inventories, rp_obj.Inventory):
+        inventories = rp_obj.InventoryList(objects=[inventories])
+    for inventory in inventories:
+        if op(inventory.capacity, 0):
+            raise exc_class(
+                resource_class=inventory.resource_class,
+                resource_provider=inventory.resource_provider.uuid)
+
+
 @wsgi_wrapper.PlacementWsgify
 @util.require_content('application/json')
 def create_inventory(req):
@@ -168,6 +194,8 @@ def create_inventory(req):
                                        **data)
 
     try:
+        _validate_inventory_capacity(
+            req.environ[microversion.MICROVERSION_ENVIRON], inventory)
         resource_provider.add_inventory(inventory)
     except (exception.ConcurrentUpdateDetected,
             db_exc.DBDuplicateEntry) as exc:
@@ -305,6 +333,8 @@ def set_inventories(req):
     inventories = rp_obj.InventoryList(objects=inv_list)
 
     try:
+        _validate_inventory_capacity(
+            req.environ[microversion.MICROVERSION_ENVIRON], inventories)
         resource_provider.set_inventory(inventories)
     except exception.ResourceClassNotFound as exc:
         raise webob.exc.HTTPBadRequest(
@@ -401,6 +431,8 @@ def update_inventory(req):
                                        **data)
 
     try:
+        _validate_inventory_capacity(
+            req.environ[microversion.MICROVERSION_ENVIRON], inventory)
         resource_provider.update_inventory(inventory)
     except (exception.ConcurrentUpdateDetected,
             db_exc.DBDuplicateEntry) as exc:
diff --git a/nova/api/openstack/placement/microversion.py b/nova/api/openstack/placement/microversion.py
index 5d2f588a58f3..e34ce0b7b4ce 100644
--- a/nova/api/openstack/placement/microversion.py
+++ b/nova/api/openstack/placement/microversion.py
@@ -68,6 +68,8 @@ VERSIONS = [
              # GET /resource_providers
     '1.25',  # Adds support for granular resource requests via numbered
              # querystring groups in GET /allocation_candidates
+    '1.26',  # Add ability to specify inventory with reserved value equal to
+             # total.
 ]
 
 
diff --git a/nova/api/openstack/placement/objects/resource_provider.py b/nova/api/openstack/placement/objects/resource_provider.py
index 784a6de242de..8cbb1587bfd6 100644
--- a/nova/api/openstack/placement/objects/resource_provider.py
+++ b/nova/api/openstack/placement/objects/resource_provider.py
@@ -201,10 +201,6 @@ def _add_inventory_to_provider(ctx, rp, inv_list, to_add):
     for rc_id in to_add:
         rc_str = _RC_CACHE.string_from_id(rc_id)
         inv_record = inv_list.find(rc_str)
-        if inv_record.capacity <= 0:
-            raise exception.InvalidInventoryCapacity(
-                resource_class=rc_str,
-                resource_provider=rp.uuid)
         ins_stmt = _INV_TBL.insert().values(
                 resource_provider_id=rp.id,
                 resource_class_id=rc_id,
@@ -232,10 +228,6 @@ def _update_inventory_for_provider(ctx, rp, inv_list, to_update):
     for rc_id in to_update:
         rc_str = _RC_CACHE.string_from_id(rc_id)
         inv_record = inv_list.find(rc_str)
-        if inv_record.capacity <= 0:
-            raise exception.InvalidInventoryCapacity(
-                resource_class=rc_str,
-                resource_provider=rp.uuid)
         allocation_query = sa.select(
             [func.sum(_ALLOC_TBL.c.used).label('usage')]).\
             where(sa.and_(
diff --git a/nova/api/openstack/placement/rest_api_version_history.rst b/nova/api/openstack/placement/rest_api_version_history.rst
index 16bde5befbb6..2673b8a9f20f 100644
--- a/nova/api/openstack/placement/rest_api_version_history.rst
+++ b/nova/api/openstack/placement/rest_api_version_history.rst
@@ -323,3 +323,9 @@ The semantic of the (unnumbered) ``resources``, ``required``, and ``member_of``
 query parameters is unchanged: the resources, traits, and aggregate
 associations specified thereby may be satisfied by any provider in the same
 non-sharing tree or associated via the specified aggregate(s).
+
+1.26 Allow inventories to have reserved value equal to total
+------------------------------------------------------------
+
+Starting with this version, it is allowed to set the reserved value of the
+resource provider inventory to be equal to total.
diff --git a/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py b/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
index b49a3736c0cc..feba1e037b5c 100644
--- a/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
+++ b/nova/tests/functional/api/openstack/placement/db/test_resource_provider.py
@@ -584,22 +584,6 @@ class ResourceProviderTestCase(tb.PlacementDbBaseTestCase):
         self.assertEqual(1, len(new_inv_list))
         self.assertEqual(2048, new_inv_list[0].total)
 
-        # fail when inventory bad
-        disk_inv = rp_obj.Inventory(
-                resource_provider=rp,
-                resource_class=fields.ResourceClass.DISK_GB,
-                total=2048,
-                reserved=2048)
-        disk_inv.obj_set_defaults()
-        error = self.assertRaises(exception.InvalidInventoryCapacity,
-                                  rp.update_inventory, disk_inv)
-        self.assertIn("Invalid inventory for '%s'"
-                      % fields.ResourceClass.DISK_GB, str(error))
-        self.assertIn("on resource provider '%s'." % rp.uuid, str(error))
-
-        # generation has not bumped
-        self.assertEqual(saved_generation, rp.generation)
-
         # delete inventory
         rp.delete_inventory(fields.ResourceClass.DISK_GB)
 
@@ -693,17 +677,6 @@ class ResourceProviderTestCase(tb.PlacementDbBaseTestCase):
         mock_log.warning.assert_called_once_with(
             mock.ANY, {'uuid': rp.uuid, 'resource': 'DISK_GB'})
 
-    def test_add_invalid_inventory(self):
-        rp = self._create_provider(uuidsentinel.rp_name)
-        error = self.assertRaises(
-            exception.InvalidInventoryCapacity,
-            tb.add_inventory, rp, fields.ResourceClass.DISK_GB, 1024,
-            reserved=2048)
-        self.assertIn("Invalid inventory for '%s'"
-                      % fields.ResourceClass.DISK_GB, str(error))
-        self.assertIn("on resource provider '%s'."
-                      % rp.uuid, str(error))
-
     def test_add_allocation_increments_generation(self):
         rp = self._create_provider(name='foo')
         tb.add_inventory(rp, DISK_INVENTORY['resource_class'],
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml b/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
index 5ab3a8390113..732f8a32ca79 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/inventory.yaml
@@ -649,9 +649,84 @@ tests:
   status: 400
   response_strings:
       - Unable to update inventory
+      - greater than or equal to total
   response_json_paths:
       $.errors[0].title: Bad Request
 
+- name: put all inventory zero capacity old microversion
+  PUT: $LAST_URL
+  request_headers:
+      content-type: application/json
+  data:
+      resource_provider_generation: 6
+      inventories:
+        IPV4_ADDRESS:
+          total: 253
+          reserved: 253
+  status: 400
+  response_strings:
+      - Unable to update inventory
+      - greater than or equal to total
+  response_json_paths:
+      $.errors[0].title: Bad Request
+
+- name: put inventory with reserved equal to total
+  PUT: $LAST_URL
+  request_headers:
+      content-type: application/json
+      openstack-api-version: placement 1.26
+  data:
+      resource_provider_generation: 6
+      inventories:
+        IPV4_ADDRESS:
+          total: 253
+          reserved: 253
+  status: 200
+
+- name: put all inventory bad capacity in new microversion
+  PUT: $LAST_URL
+  request_headers:
+      content-type: application/json
+      openstack-api-version: placement 1.26
+  data:
+      resource_provider_generation: 7
+      inventories:
+        IPV4_ADDRESS:
+          total: 253
+          reserved: 512
+  status: 400
+  response_strings:
+      - Unable to update inventory
+      - greater than total
+  response_json_paths:
+      $.errors[0].title: Bad Request
+
+- name: put one inventory zero capacity old microversion
+  PUT: /resource_providers/$ENVIRON['RP_UUID']/inventories/IPV4_ADDRESS
+  request_headers:
+      content-type: application/json
+  data:
+      resource_provider_generation: 7
+      total: 253
+      reserved: 253
+  status: 400
+  response_strings:
+      - Unable to update inventory
+      - greater than or equal to total
+  response_json_paths:
+      $.errors[0].title: Bad Request
+
+- name: put one inventory with reserved equal to total new microversion
+  PUT: $LAST_URL
+  request_headers:
+      content-type: application/json
+      openstack-api-version: placement 1.26
+  data:
+      resource_provider_generation: 7
+      total: 512
+      reserved: 512
+  status: 200
+
 - name: delete all inventory bad generation
   PUT: /resource_providers/$ENVIRON['RP_UUID']/inventories
   request_headers:
@@ -680,7 +755,7 @@ tests:
 - name: get inventories after deletions
   GET: /resource_providers/$ENVIRON['RP_UUID']/inventories
   response_json_paths:
-      $.resource_provider_generation: 8
+      $.resource_provider_generation: 10
       $.inventories: {}
 
 - name: post an inventory again
@@ -699,7 +774,7 @@ tests:
   response_headers:
       location: $SCHEME://$NETLOC/resource_providers/$ENVIRON['RP_UUID']/inventories/DISK_GB
   response_json_paths:
-      $.resource_provider_generation: 9
+      $.resource_provider_generation: 11
       $.total: 2048
       $.reserved: 512
 
@@ -709,17 +784,17 @@ tests:
       content-type: application/json
       openstack-api-version: placement 1.4
   data:
-      resource_provider_generation: 9
+      resource_provider_generation: 11
       inventories: {}
   response_json_paths:
-      $.resource_provider_generation: 10
+      $.resource_provider_generation: 12
       $.inventories: {}
   status: 200
 
 - name: get generation after deletion
   GET: /resource_providers/$ENVIRON['RP_UUID']/inventories
   response_json_paths:
-      $.resource_provider_generation: 10
+      $.resource_provider_generation: 12
       $.inventories: {}
 
 - name: delete inventories earlier version
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml b/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
index 7970eb9a7ce4..1ffd631f5cda 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml
@@ -39,13 +39,13 @@ tests:
   response_json_paths:
       $.errors[0].title: Not Acceptable
 
-- name: latest microversion is 1.25
+- name: latest microversion is 1.26
   GET: /
   request_headers:
       openstack-api-version: placement latest
   response_headers:
       vary: /openstack-api-version/
-      openstack-api-version: placement 1.25
+      openstack-api-version: placement 1.26
 
 - name: other accept header bad version
   GET: /
diff --git a/releasenotes/notes/allow-reserved-equal-total-inventory-fe93584dd28c460d.yaml b/releasenotes/notes/allow-reserved-equal-total-inventory-fe93584dd28c460d.yaml
new file mode 100644
index 000000000000..ecbeee8d4d40
--- /dev/null
+++ b/releasenotes/notes/allow-reserved-equal-total-inventory-fe93584dd28c460d.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Introduces new placement API version ``1.26``. Starting with this version
+    it is allowed to define resource provider inventories with reserved value
+    equal to total.