Do not enforce PoV size hard limit in config (#5887)

Quoting @bkchr (from
[here](#5334 (comment))):

> That the hardcoded limit is used there again, is IMO not correct. The
`max_pov_size` should be controlled by the `HostConfiguration` and not
limited by some "random" constant.

This PR aims to change the hard limit to a not-so-random constant,
allowing more room for maneuvering in the future.

polkadot/runtime/parachains/src/configuration.rs

@@ -29,7 +29,7 @@ use polkadot_parachain_primitives::primitives::{
 use polkadot_primitives::{
 	ApprovalVotingParams, AsyncBackingParams, Balance, ExecutorParamError, ExecutorParams,
 	NodeFeatures, SessionIndex, LEGACY_MIN_BACKING_VOTES, MAX_CODE_SIZE, MAX_HEAD_DATA_SIZE,
-	MAX_POV_SIZE, ON_DEMAND_MAX_QUEUE_MAX_SIZE,
+	ON_DEMAND_MAX_QUEUE_MAX_SIZE,
 };
 use sp_runtime::{traits::Zero, Perbill, Percent};
 
@@ -46,6 +46,10 @@ use polkadot_primitives::SchedulerParams;
 
 const LOG_TARGET: &str = "runtime::configuration";
 
+// This value is derived from network layer limits. See `sc_network::MAX_RESPONSE_SIZE` and
+// `polkadot_node_network_protocol::POV_RESPONSE_SIZE`.
+const POV_SIZE_HARD_LIMIT: u32 = 16 * 1024 * 1024;
+
 /// All configuration of the runtime with respect to paras.
 #[derive(
 	Clone,
@@ -310,7 +314,7 @@ pub enum InconsistentError<BlockNumber> {
 	MaxCodeSizeExceedHardLimit { max_code_size: u32 },
 	/// `max_head_data_size` exceeds the hard limit of `MAX_HEAD_DATA_SIZE`.
 	MaxHeadDataSizeExceedHardLimit { max_head_data_size: u32 },
-	/// `max_pov_size` exceeds the hard limit of `MAX_POV_SIZE`.
+	/// `max_pov_size` exceeds the hard limit of `POV_SIZE_HARD_LIMIT`.
 	MaxPovSizeExceedHardLimit { max_pov_size: u32 },
 	/// `minimum_validation_upgrade_delay` is less than `paras_availability_period`.
 	MinimumValidationUpgradeDelayLessThanChainAvailabilityPeriod {
@@ -377,7 +381,7 @@ where
 			})
 		}
 
-		if self.max_pov_size > MAX_POV_SIZE {
+		if self.max_pov_size > POV_SIZE_HARD_LIMIT {
 			return Err(MaxPovSizeExceedHardLimit { max_pov_size: self.max_pov_size })
 		}
 

polkadot/runtime/parachains/src/configuration/tests.rs

@@ -210,7 +210,7 @@ fn invariants() {
 		);
 
 		assert_err!(
-			Configuration::set_max_pov_size(RuntimeOrigin::root(), MAX_POV_SIZE + 1),
+			Configuration::set_max_pov_size(RuntimeOrigin::root(), POV_SIZE_HARD_LIMIT + 1),
 			Error::<Test>::InvalidNewValue
 		);
 

prdoc/pr_5887.prdoc

@@ -0,0 +1,17 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: "Set reasonable hard limit for PoV size config value"
+
+doc:
+  - audience:
+    - Runtime Dev
+    - Runtime User
+    description: |
+      Sets the hard limit of the `max_pov_size` host configuration parameter to correspond to the
+      actual network-related limit rather than to a random constant.
+
+crates:
+  - name: polkadot-runtime-parachains
+    bump: patch
+