Elastic scaling: use an assumed CoreIndex in candidate-backing (#3229)

First step in implementing
https://github.com/paritytech/polkadot-sdk/issues/3144

### Summary of changes
- switch statement `Table` candidate mapping from `ParaId` to
`CoreIndex`
- introduce experimental `InjectCoreIndex`  node feature.
- determine and assume a `CoreIndex` for a candidate based on statement
validator index. If the signature is valid it means validator controls
the validator that index and we can easily map it to a validator
group/core.
- introduce a temporary provisioner fix until we fully enable elastic
scaling in the subystem. The fix ensures we don't fetch the same
backable candidate when calling `get_backable_candidate` for each core.

TODO:
- [x] fix backing tests
- [x] fix statement table tests
- [x] add new test

---------

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>
Signed-off-by: alindima <alin@parity.io>
Co-authored-by: alindima <alin@parity.io>

Cargo.lock

@@ -12490,6 +12490,7 @@ dependencies = [
  "polkadot-primitives-test-helpers",
  "polkadot-statement-table",
  "sc-keystore",
+ "schnellru",
  "sp-application-crypto",
  "sp-core",
  "sp-keyring",
@@ -13159,6 +13160,7 @@ version = "7.0.0"
 dependencies = [
  "bitvec",
  "hex-literal",
+ "log",
  "parity-scale-codec",
  "polkadot-core-primitives",
  "polkadot-parachain-primitives",
@@ -13556,6 +13558,7 @@ dependencies = [
  "parity-scale-codec",
  "polkadot-primitives",
  "sp-core",
+ "tracing-gum",
 ]
 
 [[package]]

polkadot/node/core/backing/Cargo.toml

@@ -22,6 +22,7 @@ bitvec = { version = "1.0.0", default-features = false, features = ["alloc"] }
 gum = { package = "tracing-gum", path = "../../gum" }
 thiserror = { workspace = true }
 fatality = "0.0.6"
+schnellru = "0.2.1"
 
 [dev-dependencies]
 sp-core = { path = "../../../../substrate/primitives/core" }

polkadot/node/core/backing/src/error.rs

@@ -48,6 +48,9 @@ pub enum Error {
 	#[error("Candidate is not found")]
 	CandidateNotFound,
 
+	#[error("CoreIndex cannot be determined for a candidate")]
+	CoreIndexUnavailable,
+
 	#[error("Signature is invalid")]
 	InvalidSignature,
 

polkadot/node/core/backing/src/lib.rs

@@ -70,13 +70,14 @@ use std::{
 	sync::Arc,
 };
 
-use bitvec::vec::BitVec;
+use bitvec::{order::Lsb0 as BitOrderLsb0, vec::BitVec};
 use futures::{
 	channel::{mpsc, oneshot},
 	future::BoxFuture,
 	stream::FuturesOrdered,
 	FutureExt, SinkExt, StreamExt, TryFutureExt,
 };
+use schnellru::{ByLength, LruMap};
 
 use error::{Error, FatalResult};
 use polkadot_node_primitives::{
@@ -104,10 +105,12 @@ use polkadot_node_subsystem_util::{
 	Validator,
 };
 use polkadot_primitives::{
+	vstaging::{node_features::FeatureIndex, NodeFeatures},
 	BackedCandidate, CandidateCommitments, CandidateHash, CandidateReceipt,
-	CommittedCandidateReceipt, CoreIndex, CoreState, ExecutorParams, Hash, Id as ParaId,
+	CommittedCandidateReceipt, CoreIndex, CoreState, ExecutorParams, GroupIndex, GroupRotationInfo,
-	PersistedValidationData, PvfExecKind, SigningContext, ValidationCode, ValidatorId,
+	Hash, Id as ParaId, IndexedVec, PersistedValidationData, PvfExecKind, SessionIndex,
-	ValidatorIndex, ValidatorSignature, ValidityAttestation,
+	SigningContext, ValidationCode, ValidatorId, ValidatorIndex, ValidatorSignature,
+	ValidityAttestation,
 };
 use sp_keystore::KeystorePtr;
 use statement_table::{
@@ -118,7 +121,7 @@ use statement_table::{
 	},
 	Config as TableConfig, Context as TableContextTrait, Table,
 };
-use util::vstaging::get_disabled_validators_with_fallback;
+use util::{runtime::request_node_features, vstaging::get_disabled_validators_with_fallback};
 
 mod error;
 
@@ -209,7 +212,9 @@ struct PerRelayParentState {
 	/// The hash of the relay parent on top of which this job is doing it's work.
 	parent: Hash,
 	/// The `ParaId` assigned to the local validator at this relay parent.
-	assignment: Option<ParaId>,
+	assigned_para: Option<ParaId>,
+	/// The `CoreIndex` assigned to the local validator at this relay parent.
+	assigned_core: Option<CoreIndex>,
 	/// The candidates that are backed by enough validators in their group, by hash.
 	backed: HashSet<CandidateHash>,
 	/// The table of candidates and statements under this relay-parent.
@@ -224,6 +229,15 @@ struct PerRelayParentState {
 	fallbacks: HashMap<CandidateHash, AttestingData>,
 	/// The minimum backing votes threshold.
 	minimum_backing_votes: u32,
+	/// If true, we're appending extra bits in the BackedCandidate validator indices bitfield,
+	/// which represent the assigned core index. True if ElasticScalingMVP is enabled.
+	inject_core_index: bool,
+	/// The core states for all cores.
+	cores: Vec<CoreState>,
+	/// The validator index -> group mapping at this relay parent.
+	validator_to_group: Arc<IndexedVec<ValidatorIndex, Option<GroupIndex>>>,
+	/// The associated group rotation information.
+	group_rotation_info: GroupRotationInfo,
 }
 
 struct PerCandidateState {
@@ -275,6 +289,9 @@ struct State {
 	/// This is guaranteed to have an entry for each candidate with a relay parent in the implicit
 	/// or explicit view for which a `Seconded` statement has been successfully imported.
 	per_candidate: HashMap<CandidateHash, PerCandidateState>,
+	/// Cache the per-session Validator->Group mapping.
+	validator_to_group_cache:
+		LruMap<SessionIndex, Arc<IndexedVec<ValidatorIndex, Option<GroupIndex>>>>,
 	/// A cloneable sender which is dispatched to background candidate validation tasks to inform
 	/// the main task of the result.
 	background_validation_tx: mpsc::Sender<(Hash, ValidatedCandidateCommand)>,
@@ -292,6 +309,7 @@ impl State {
 			per_leaf: HashMap::default(),
 			per_relay_parent: HashMap::default(),
 			per_candidate: HashMap::new(),
+			validator_to_group_cache: LruMap::new(ByLength::new(2)),
 			background_validation_tx,
 			keystore,
 		}
@@ -379,10 +397,10 @@ struct AttestingData {
 	backing: Vec<ValidatorIndex>,
 }
 
-#[derive(Default)]
+#[derive(Default, Debug)]
 struct TableContext {
 	validator: Option<Validator>,
-	groups: HashMap<ParaId, Vec<ValidatorIndex>>,
+	groups: HashMap<CoreIndex, Vec<ValidatorIndex>>,
 	validators: Vec<ValidatorId>,
 	disabled_validators: Vec<ValidatorIndex>,
 }
@@ -404,7 +422,7 @@ impl TableContext {
 impl TableContextTrait for TableContext {
 	type AuthorityId = ValidatorIndex;
 	type Digest = CandidateHash;
-	type GroupId = ParaId;
+	type GroupId = CoreIndex;
 	type Signature = ValidatorSignature;
 	type Candidate = CommittedCandidateReceipt;
 
@@ -412,15 +430,11 @@ impl TableContextTrait for TableContext {
 		candidate.hash()
 	}
 
-	fn candidate_group(candidate: &CommittedCandidateReceipt) -> ParaId {
+	fn is_member_of(&self, authority: &ValidatorIndex, core: &CoreIndex) -> bool {
-		candidate.descriptor().para_id
+		self.groups.get(core).map_or(false, |g| g.iter().any(|a| a == authority))
 	}
 
-	fn is_member_of(&self, authority: &ValidatorIndex, group: &ParaId) -> bool {
+	fn get_group_size(&self, group: &CoreIndex) -> Option<usize> {
-		self.groups.get(group).map_or(false, |g| g.iter().any(|a| a == authority))
-	}
-
-	fn get_group_size(&self, group: &ParaId) -> Option<usize> {
 		self.groups.get(group).map(|g| g.len())
 	}
 }
@@ -442,19 +456,20 @@ fn primitive_statement_to_table(s: &SignedFullStatementWithPVD) -> TableSignedSt
 
 fn table_attested_to_backed(
 	attested: TableAttestedCandidate<
-		ParaId,
+		CoreIndex,
 		CommittedCandidateReceipt,
 		ValidatorIndex,
 		ValidatorSignature,
 	>,
 	table_context: &TableContext,
+	inject_core_index: bool,
 ) -> Option<BackedCandidate> {
-	let TableAttestedCandidate { candidate, validity_votes, group_id: para_id } = attested;
+	let TableAttestedCandidate { candidate, validity_votes, group_id: core_index } = attested;
 
 	let (ids, validity_votes): (Vec<_>, Vec<ValidityAttestation>) =
 		validity_votes.into_iter().map(|(id, vote)| (id, vote.into())).unzip();
 
-	let group = table_context.groups.get(&para_id)?;
+	let group = table_context.groups.get(&core_index)?;
 
 	let mut validator_indices = BitVec::with_capacity(group.len());
 
@@ -479,6 +494,12 @@ fn table_attested_to_backed(
 	}
 	vote_positions.sort_by_key(|(_orig, pos_in_group)| *pos_in_group);
 
+	if inject_core_index {
+		let core_index_to_inject: BitVec<u8, BitOrderLsb0> =
+			BitVec::from_vec(vec![core_index.0 as u8]);
+		validator_indices.extend(core_index_to_inject);
+	}
+
 	Some(BackedCandidate {
 		candidate,
 		validity_votes: vote_positions
@@ -971,7 +992,14 @@ async fn handle_active_leaves_update<Context>(
 
 		// construct a `PerRelayParent` from the runtime API
 		// and insert it.
-		let per = construct_per_relay_parent_state(ctx, maybe_new, &state.keystore, mode).await?;
+		let per = construct_per_relay_parent_state(
+			ctx,
+			maybe_new,
+			&state.keystore,
+			&mut state.validator_to_group_cache,
+			mode,
+		)
+		.await?;
 
 		if let Some(per) = per {
 			state.per_relay_parent.insert(maybe_new, per);
@@ -981,31 +1009,112 @@ async fn handle_active_leaves_update<Context>(
 	Ok(())
 }
 
+macro_rules! try_runtime_api {
+	($x: expr) => {
+		match $x {
+			Ok(x) => x,
+			Err(err) => {
+				// Only bubble up fatal errors.
+				error::log_error(Err(Into::<runtime::Error>::into(err).into()))?;
+
+				// We can't do candidate validation work if we don't have the
+				// requisite runtime API data. But these errors should not take
+				// down the node.
+				return Ok(None)
+			},
+		}
+	};
+}
+
+fn core_index_from_statement(
+	validator_to_group: &IndexedVec<ValidatorIndex, Option<GroupIndex>>,
+	group_rotation_info: &GroupRotationInfo,
+	cores: &[CoreState],
+	statement: &SignedFullStatementWithPVD,
+) -> Option<CoreIndex> {
+	let compact_statement = statement.as_unchecked();
+	let candidate_hash = CandidateHash(*compact_statement.unchecked_payload().candidate_hash());
+
+	let n_cores = cores.len();
+
+	gum::trace!(
+		target:LOG_TARGET,
+		?group_rotation_info,
+		?statement,
+		?validator_to_group,
+		n_cores = ?cores.len(),
+		?candidate_hash,
+		"Extracting core index from statement"
+	);
+
+	let statement_validator_index = statement.validator_index();
+	let Some(Some(group_index)) = validator_to_group.get(statement_validator_index) else {
+		gum::debug!(
+			target: LOG_TARGET,
+			?group_rotation_info,
+			?statement,
+			?validator_to_group,
+			n_cores = ?cores.len() ,
+			?candidate_hash,
+			"Invalid validator index: {:?}",
+			statement_validator_index
+		);
+		return None
+	};
+
+	// First check if the statement para id matches the core assignment.
+	let core_index = group_rotation_info.core_for_group(*group_index, n_cores);
+
+	if core_index.0 as usize > n_cores {
+		gum::warn!(target: LOG_TARGET, ?candidate_hash, ?core_index, n_cores, "Invalid CoreIndex");
+		return None
+	}
+
+	if let StatementWithPVD::Seconded(candidate, _pvd) = statement.payload() {
+		let candidate_para_id = candidate.descriptor.para_id;
+		let assigned_para_id = match &cores[core_index.0 as usize] {
+			CoreState::Free => {
+				gum::debug!(target: LOG_TARGET, ?candidate_hash, "Invalid CoreIndex, core is not assigned to any para_id");
+				return None
+			},
+			CoreState::Occupied(occupied) =>
+				if let Some(next) = &occupied.next_up_on_available {
+					next.para_id
+				} else {
+					return None
+				},
+			CoreState::Scheduled(scheduled) => scheduled.para_id,
+		};
+
+		if assigned_para_id != candidate_para_id {
+			gum::debug!(
+				target: LOG_TARGET,
+				?candidate_hash,
+				?core_index,
+				?assigned_para_id,
+				?candidate_para_id,
+				"Invalid CoreIndex, core is assigned to a different para_id"
+			);
+			return None
+		}
+		return Some(core_index)
+	} else {
+		return Some(core_index)
+	}
+}
+
 /// Load the data necessary to do backing work on top of a relay-parent.
 #[overseer::contextbounds(CandidateBacking, prefix = self::overseer)]
 async fn construct_per_relay_parent_state<Context>(
 	ctx: &mut Context,
 	relay_parent: Hash,
 	keystore: &KeystorePtr,
+	validator_to_group_cache: &mut LruMap<
+		SessionIndex,
+		Arc<IndexedVec<ValidatorIndex, Option<GroupIndex>>>,
+	>,
 	mode: ProspectiveParachainsMode,
 ) -> Result<Option<PerRelayParentState>, Error> {
-	macro_rules! try_runtime_api {
-		($x: expr) => {
-			match $x {
-				Ok(x) => x,
-				Err(err) => {
-					// Only bubble up fatal errors.
-					error::log_error(Err(Into::<runtime::Error>::into(err).into()))?;
-
-					// We can't do candidate validation work if we don't have the
-					// requisite runtime API data. But these errors should not take
-					// down the node.
-					return Ok(None)
-				},
-			}
-		};
-	}
-
 	let parent = relay_parent;
 
 	let (session_index, validators, groups, cores) = futures::try_join!(
@@ -1020,6 +1129,16 @@ async fn construct_per_relay_parent_state<Context>(
 	.map_err(Error::JoinMultiple)?;
 
 	let session_index = try_runtime_api!(session_index);
+
+	let inject_core_index = request_node_features(parent, session_index, ctx.sender())
+		.await?
+		.unwrap_or(NodeFeatures::EMPTY)
+		.get(FeatureIndex::ElasticScalingMVP as usize)
+		.map(|b| *b)
+		.unwrap_or(false);
+
+	gum::debug!(target: LOG_TARGET, inject_core_index, ?parent, "New state");
+
 	let validators: Vec<_> = try_runtime_api!(validators);
 	let (validator_groups, group_rotation_info) = try_runtime_api!(groups);
 	let cores = try_runtime_api!(cores);
@@ -1055,18 +1174,24 @@ async fn construct_per_relay_parent_state<Context>(
 		},
 	};
 
-	let mut groups = HashMap::new();
 	let n_cores = cores.len();
-	let mut assignment = None;
 
-	for (idx, core) in cores.into_iter().enumerate() {
+	let mut groups = HashMap::<CoreIndex, Vec<ValidatorIndex>>::new();
+	let mut assigned_core = None;
+	let mut assigned_para = None;
+
+	for (idx, core) in cores.iter().enumerate() {
 		let core_para_id = match core {
 			CoreState::Scheduled(scheduled) => scheduled.para_id,
 			CoreState::Occupied(occupied) =>
 				if mode.is_enabled() {
 					// Async backing makes it legal to build on top of
 					// occupied core.
-					occupied.candidate_descriptor.para_id
+					if let Some(next) = &occupied.next_up_on_available {
+						next.para_id
+					} else {
+						continue
+					}
 				} else {
 					continue
 				},
@@ -1077,11 +1202,27 @@ async fn construct_per_relay_parent_state<Context>(
 		let group_index = group_rotation_info.group_for_core(core_index, n_cores);
 		if let Some(g) = validator_groups.get(group_index.0 as usize) {
 			if validator.as_ref().map_or(false, |v| g.contains(&v.index())) {
-				assignment = Some(core_para_id);
+				assigned_para = Some(core_para_id);
+				assigned_core = Some(core_index);
 			}
-			groups.insert(core_para_id, g.clone());
+			groups.insert(core_index, g.clone());
 		}
 	}
+	gum::debug!(target: LOG_TARGET, ?groups, "TableContext");
+
+	let validator_to_group = validator_to_group_cache
+		.get_or_insert(session_index, || {
+			let mut vector = vec![None; validators.len()];
+
+			for (group_idx, validator_group) in validator_groups.iter().enumerate() {
+				for validator in validator_group {
+					vector[validator.0 as usize] = Some(GroupIndex(group_idx as u32));
+				}
+			}
+
+			Arc::new(IndexedVec::<_, _>::from(vector))
+		})
+		.expect("Just inserted");
 
 	let table_context = TableContext { validator, groups, validators, disabled_validators };
 	let table_config = TableConfig {
@@ -1094,7 +1235,8 @@ async fn construct_per_relay_parent_state<Context>(
 	Ok(Some(PerRelayParentState {
 		prospective_parachains_mode: mode,
 		parent,
-		assignment,
+		assigned_core,
+		assigned_para,
 		backed: HashSet::new(),
 		table: Table::new(table_config),
 		table_context,
@@ -1102,6 +1244,10 @@ async fn construct_per_relay_parent_state<Context>(
 		awaiting_validation: HashSet::new(),
 		fallbacks: HashMap::new(),
 		minimum_backing_votes,
+		inject_core_index,
+		cores,
+		validator_to_group: validator_to_group.clone(),
+		group_rotation_info,
 	}))
 }
 
@@ -1519,15 +1665,16 @@ async fn import_statement<Context>(
 	per_candidate: &mut HashMap<CandidateHash, PerCandidateState>,
 	statement: &SignedFullStatementWithPVD,
 ) -> Result<Option<TableSummary>, Error> {
+	let candidate_hash = statement.payload().candidate_hash();
+
 	gum::debug!(
 		target: LOG_TARGET,
 		statement = ?statement.payload().to_compact(),
 		validator_index = statement.validator_index().0,
+		?candidate_hash,
 		"Importing statement",
 	);
 
-	let candidate_hash = statement.payload().candidate_hash();
-
 	// If this is a new candidate (statement is 'seconded' and candidate is unknown),
 	// we need to create an entry in the `PerCandidateState` map.
 	//
@@ -1593,7 +1740,15 @@ async fn import_statement<Context>(
 
 	let stmt = primitive_statement_to_table(statement);
 
-	Ok(rp_state.table.import_statement(&rp_state.table_context, stmt))
+	let core = core_index_from_statement(
+		&rp_state.validator_to_group,
+		&rp_state.group_rotation_info,
+		&rp_state.cores,
+		statement,
+	)
+	.ok_or(Error::CoreIndexUnavailable)?;
+
+	Ok(rp_state.table.import_statement(&rp_state.table_context, core, stmt))
 }
 
 /// Handles a summary received from [`import_statement`] and dispatches `Backed` notifications and
@@ -1615,7 +1770,11 @@ async fn post_import_statement_actions<Context>(
 
 		// `HashSet::insert` returns true if the thing wasn't in there already.
 		if rp_state.backed.insert(candidate_hash) {
-			if let Some(backed) = table_attested_to_backed(attested, &rp_state.table_context) {
+			if let Some(backed) = table_attested_to_backed(
+				attested,
+				&rp_state.table_context,
+				rp_state.inject_core_index,
+			) {
 				let para_id = backed.candidate.descriptor.para_id;
 				gum::debug!(
 					target: LOG_TARGET,
@@ -1654,8 +1813,14 @@ async fn post_import_statement_actions<Context>(
 					);
 					ctx.send_unbounded_message(message);
 				}
+			} else {
+				gum::debug!(target: LOG_TARGET, ?candidate_hash, "Cannot get BackedCandidate");
 			}
+		} else {
+			gum::debug!(target: LOG_TARGET, ?candidate_hash, "Candidate already known");
 		}
+	} else {
+		gum::debug!(target: LOG_TARGET, "No attested candidate");
 	}
 
 	issue_new_misbehaviors(ctx, rp_state.parent, &mut rp_state.table);
@@ -1859,9 +2024,10 @@ async fn maybe_validate_and_import<Context>(
 
 		let candidate_hash = summary.candidate;
 
-		if Some(summary.group_id) != rp_state.assignment {
+		if Some(summary.group_id) != rp_state.assigned_core {
 			return Ok(())
 		}
+
 		let attesting = match statement.payload() {
 			StatementWithPVD::Seconded(receipt, _) => {
 				let attesting = AttestingData {
@@ -2004,10 +2170,11 @@ async fn handle_second_message<Context>(
 	}
 
 	// Sanity check that candidate is from our assignment.
-	if Some(candidate.descriptor().para_id) != rp_state.assignment {
+	if Some(candidate.descriptor().para_id) != rp_state.assigned_para {
 		gum::debug!(
 			target: LOG_TARGET,
-			our_assignment = ?rp_state.assignment,
+			our_assignment_core = ?rp_state.assigned_core,
+			our_assignment_para = ?rp_state.assigned_para,
 			collation = ?candidate.descriptor().para_id,
 			"Subsystem asked to second for para outside of our assignment",
 		);
@@ -2015,6 +2182,14 @@ async fn handle_second_message<Context>(
 		return Ok(())
 	}
 
+	gum::debug!(
+		target: LOG_TARGET,
+		our_assignment_core = ?rp_state.assigned_core,
+		our_assignment_para = ?rp_state.assigned_para,
+		collation = ?candidate.descriptor().para_id,
+		"Current assignments vs collation",
+	);
+
 	// If the message is a `CandidateBackingMessage::Second`, sign and dispatch a
 	// Seconded statement only if we have not signed a Valid statement for the requested candidate.
 	//
@@ -2087,7 +2262,13 @@ fn handle_get_backed_candidates_message(
 					&rp_state.table_context,
 					rp_state.minimum_backing_votes,
 				)
-				.and_then(|attested| table_attested_to_backed(attested, &rp_state.table_context))
+				.and_then(|attested| {
+					table_attested_to_backed(
+						attested,
+						&rp_state.table_context,
+						rp_state.inject_core_index,
+					)
+				})
 		})
 		.collect();
 

polkadot/node/core/backing/src/tests/mod.rs

@@ -65,13 +65,14 @@ fn dummy_pvd() -> PersistedValidationData {
 	}
 }
 
-struct TestState {
+pub(crate) struct TestState {
 	chain_ids: Vec<ParaId>,
 	keystore: KeystorePtr,
 	validators: Vec<Sr25519Keyring>,
 	validator_public: Vec<ValidatorId>,
 	validation_data: PersistedValidationData,
 	validator_groups: (Vec<Vec<ValidatorIndex>>, GroupRotationInfo),
+	validator_to_group: IndexedVec<ValidatorIndex, Option<GroupIndex>>,
 	availability_cores: Vec<CoreState>,
 	head_data: HashMap<ParaId, HeadData>,
 	signing_context: SigningContext,
@@ -114,6 +115,11 @@ impl Default for TestState {
 			.into_iter()
 			.map(|g| g.into_iter().map(ValidatorIndex).collect())
 			.collect();
+		let validator_to_group: IndexedVec<_, _> =
+			vec![Some(0), Some(1), Some(0), Some(0), None, Some(0)]
+				.into_iter()
+				.map(|x| x.map(|x| GroupIndex(x)))
+				.collect();
 		let group_rotation_info =
 			GroupRotationInfo { session_start_block: 0, group_rotation_frequency: 100, now: 1 };
 
@@ -143,6 +149,7 @@ impl Default for TestState {
 			validators,
 			validator_public,
 			validator_groups: (validator_groups, group_rotation_info),
+			validator_to_group,
 			availability_cores,
 			head_data,
 			validation_data,
@@ -285,6 +292,16 @@ async fn test_startup(virtual_overseer: &mut VirtualOverseer, test_state: &TestS
 		}
 	);
 
+	// Node features request from runtime: all features are disabled.
+	assert_matches!(
+		virtual_overseer.recv().await,
+		AllMessages::RuntimeApi(
+			RuntimeApiMessage::Request(_parent, RuntimeApiRequest::NodeFeatures(_session_index, tx))
+		) => {
+			tx.send(Ok(Default::default())).unwrap();
+		}
+	);
+
 	// Check if subsystem job issues a request for the minimum backing votes.
 	assert_matches!(
 		virtual_overseer.recv().await,
@@ -639,6 +656,107 @@ fn backing_works() {
 	});
 }
 
+#[test]
+fn extract_core_index_from_statement_works() {
+	let test_state = TestState::default();
+
+	let pov_a = PoV { block_data: BlockData(vec![42, 43, 44]) };
+	let pvd_a = dummy_pvd();
+	let validation_code_a = ValidationCode(vec![1, 2, 3]);
+
+	let pov_hash = pov_a.hash();
+
+	let mut candidate = TestCandidateBuilder {
+		para_id: test_state.chain_ids[0],
+		relay_parent: test_state.relay_parent,
+		pov_hash,
+		erasure_root: make_erasure_root(&test_state, pov_a.clone(), pvd_a.clone()),
+		persisted_validation_data_hash: pvd_a.hash(),
+		validation_code: validation_code_a.0.clone(),
+		..Default::default()
+	}
+	.build();
+
+	let public2 = Keystore::sr25519_generate_new(
+		&*test_state.keystore,
+		ValidatorId::ID,
+		Some(&test_state.validators[2].to_seed()),
+	)
+	.expect("Insert key into keystore");
+
+	let signed_statement_1 = SignedFullStatementWithPVD::sign(
+		&test_state.keystore,
+		StatementWithPVD::Seconded(candidate.clone(), pvd_a.clone()),
+		&test_state.signing_context,
+		ValidatorIndex(2),
+		&public2.into(),
+	)
+	.ok()
+	.flatten()
+	.expect("should be signed");
+
+	let public1 = Keystore::sr25519_generate_new(
+		&*test_state.keystore,
+		ValidatorId::ID,
+		Some(&test_state.validators[1].to_seed()),
+	)
+	.expect("Insert key into keystore");
+
+	let signed_statement_2 = SignedFullStatementWithPVD::sign(
+		&test_state.keystore,
+		StatementWithPVD::Seconded(candidate.clone(), pvd_a.clone()),
+		&test_state.signing_context,
+		ValidatorIndex(1),
+		&public1.into(),
+	)
+	.ok()
+	.flatten()
+	.expect("should be signed");
+
+	candidate.descriptor.para_id = test_state.chain_ids[1];
+
+	let signed_statement_3 = SignedFullStatementWithPVD::sign(
+		&test_state.keystore,
+		StatementWithPVD::Seconded(candidate, pvd_a.clone()),
+		&test_state.signing_context,
+		ValidatorIndex(1),
+		&public1.into(),
+	)
+	.ok()
+	.flatten()
+	.expect("should be signed");
+
+	let core_index_1 = core_index_from_statement(
+		&test_state.validator_to_group,
+		&test_state.validator_groups.1,
+		&test_state.availability_cores,
+		&signed_statement_1,
+	)
+	.unwrap();
+
+	assert_eq!(core_index_1, CoreIndex(0));
+
+	let core_index_2 = core_index_from_statement(
+		&test_state.validator_to_group,
+		&test_state.validator_groups.1,
+		&test_state.availability_cores,
+		&signed_statement_2,
+	);
+
+	// Must be none, para_id in descriptor is different than para assigned to core
+	assert_eq!(core_index_2, None);
+
+	let core_index_3 = core_index_from_statement(
+		&test_state.validator_to_group,
+		&test_state.validator_groups.1,
+		&test_state.availability_cores,
+		&signed_statement_3,
+	)
+	.unwrap();
+
+	assert_eq!(core_index_3, CoreIndex(1));
+}
+
 #[test]
 fn backing_works_while_validation_ongoing() {
 	let test_state = TestState::default();
@@ -1422,7 +1540,7 @@ fn backing_works_after_failed_validation() {
 fn candidate_backing_reorders_votes() {
 	use sp_core::Encode;
 
-	let para_id = ParaId::from(10);
+	let core_idx = CoreIndex(10);
 	let validators = vec![
 		Sr25519Keyring::Alice,
 		Sr25519Keyring::Bob,
@@ -1436,7 +1554,7 @@ fn candidate_backing_reorders_votes() {
 	let validator_groups = {
 		let mut validator_groups = HashMap::new();
 		validator_groups
-			.insert(para_id, vec![0, 1, 2, 3, 4, 5].into_iter().map(ValidatorIndex).collect());
+			.insert(core_idx, vec![0, 1, 2, 3, 4, 5].into_iter().map(ValidatorIndex).collect());
 		validator_groups
 	};
 
@@ -1466,10 +1584,10 @@ fn candidate_backing_reorders_votes() {
 			(ValidatorIndex(3), fake_attestation(3)),
 			(ValidatorIndex(1), fake_attestation(1)),
 		],
-		group_id: para_id,
+		group_id: core_idx,
 	};
 
-	let backed = table_attested_to_backed(attested, &table_context).unwrap();
+	let backed = table_attested_to_backed(attested, &table_context, false).unwrap();
 
 	let expected_bitvec = {
 		let mut validator_indices = BitVec::<u8, bitvec::order::Lsb0>::with_capacity(6);

polkadot/node/core/backing/src/tests/prospective_parachains.rs

@@ -185,6 +185,16 @@ async fn activate_leaf(
 			}
 		);
 
+		// Node features request from runtime: all features are disabled.
+		assert_matches!(
+			virtual_overseer.recv().await,
+			AllMessages::RuntimeApi(
+				RuntimeApiMessage::Request(parent, RuntimeApiRequest::NodeFeatures(_session_index, tx))
+			) if parent == hash => {
+				tx.send(Ok(Default::default())).unwrap();
+			}
+		);
+
 		// Check if subsystem job issues a request for the minimum backing votes.
 		assert_matches!(
 			virtual_overseer.recv().await,
@@ -305,10 +315,11 @@ async fn assert_hypothetical_frontier_requests(
 			) => {
 				let idx = match expected_requests.iter().position(|r| r.0 == request) {
 					Some(idx) => idx,
-					None => panic!(
+					None =>
+						panic!(
 						"unexpected hypothetical frontier request, no match found for {:?}",
 						request
-					),
+						),
 				};
 				let resp = std::mem::take(&mut expected_requests[idx].1);
 				tx.send(resp).unwrap();
@@ -1268,6 +1279,7 @@ fn concurrent_dependent_candidates() {
 		let statement_b = CandidateBackingMessage::Statement(leaf_parent, signed_b.clone());
 
 		virtual_overseer.send(FromOrchestra::Communication { msg: statement_a }).await;
+
 		// At this point the subsystem waits for response, the previous message is received,
 		// send a second one without blocking.
 		let _ = virtual_overseer
@@ -1388,7 +1400,19 @@ fn concurrent_dependent_candidates() {
 					assert_eq!(sess_idx, 1);
 					tx.send(Ok(Some(ExecutorParams::default()))).unwrap();
 				},
+				AllMessages::RuntimeApi(RuntimeApiMessage::Request(
+					_parent,
+					RuntimeApiRequest::ValidatorGroups(tx),
+				)) => {
+					tx.send(Ok(test_state.validator_groups.clone())).unwrap();
+				},
 
+				AllMessages::RuntimeApi(RuntimeApiMessage::Request(
+					_parent,
+					RuntimeApiRequest::AvailabilityCores(tx),
+				)) => {
+					tx.send(Ok(test_state.availability_cores.clone())).unwrap();
+				},
 				_ => panic!("unexpected message received from overseer: {:?}", msg),
 			}
 		}
@@ -1419,7 +1443,6 @@ fn seconding_sanity_check_occupy_same_depth() {
 		let leaf_parent = get_parent_hash(leaf_hash);
 
 		let activated = new_leaf(leaf_hash, LEAF_BLOCK_NUMBER);
-
 		let min_block_number = LEAF_BLOCK_NUMBER - LEAF_ANCESTRY_LEN;
 		let min_relay_parents = vec![(para_id_a, min_block_number), (para_id_b, min_block_number)];
 		let test_leaf_a = TestLeaf { activated, min_relay_parents };
@@ -1555,13 +1578,14 @@ fn occupied_core_assignment() {
 		const LEAF_A_BLOCK_NUMBER: BlockNumber = 100;
 		const LEAF_A_ANCESTRY_LEN: BlockNumber = 3;
 		let para_id = test_state.chain_ids[0];
+		let previous_para_id = test_state.chain_ids[1];
 
 		// Set the core state to occupied.
 		let mut candidate_descriptor = ::test_helpers::dummy_candidate_descriptor(Hash::zero());
-		candidate_descriptor.para_id = para_id;
+		candidate_descriptor.para_id = previous_para_id;
 		test_state.availability_cores[0] = CoreState::Occupied(OccupiedCore {
 			group_responsible: Default::default(),
-			next_up_on_available: None,
+			next_up_on_available: Some(ScheduledCore { para_id, collator: None }),
 			occupied_since: 100_u32,
 			time_out_at: 200_u32,
 			next_up_on_time_out: None,

polkadot/node/core/provisioner/src/lib.rs

@@ -681,10 +681,17 @@ async fn request_backable_candidates(
 			CoreState::Free => continue,
 		};
 
+		// We should be calling this once per para rather than per core.
+		// TODO: Will be fixed in https://github.com/paritytech/polkadot-sdk/pull/3233.
+		// For now, at least make sure we don't supply the same candidate multiple times in case a
+		// para has multiple cores scheduled.
 		let response = get_backable_candidate(relay_parent, para_id, required_path, sender).await?;
-
 		match response {
-			Some((hash, relay_parent)) => selected_candidates.push((hash, relay_parent)),
+			Some((hash, relay_parent)) => {
+				if !selected_candidates.iter().any(|bc| &(hash, relay_parent) == bc) {
+					selected_candidates.push((hash, relay_parent))
+				}
+			},
 			None => {
 				gum::debug!(
 					target: LOG_TARGET,
@@ -726,6 +733,7 @@ async fn select_candidates(
 			)
 			.await?,
 	};
+	gum::debug!(target: LOG_TARGET, ?selected_candidates, "Got backable candidates");
 
 	// now get the backed candidates corresponding to these candidate receipts
 	let (tx, rx) = oneshot::channel();

polkadot/primitives/Cargo.toml

@@ -14,6 +14,7 @@ bitvec = { version = "1.0.0", default-features = false, features = ["alloc", "se
 hex-literal = "0.4.1"
 parity-scale-codec = { version = "3.6.1", default-features = false, features = ["bit-vec", "derive"] }
 scale-info = { version = "2.10.0", default-features = false, features = ["bit-vec", "derive", "serde"] }
+log = { workspace = true, default-features = false }
 serde = { features = ["alloc", "derive"], workspace = true }
 
 application-crypto = { package = "sp-application-crypto", path = "../../substrate/primitives/application-crypto", default-features = false, features = ["serde"] }
@@ -38,6 +39,7 @@ std = [
 	"application-crypto/std",
 	"bitvec/std",
 	"inherents/std",
+	"log/std",
 	"parity-scale-codec/std",
 	"polkadot-core-primitives/std",
 	"polkadot-parachain-primitives/std",

polkadot/primitives/src/v6/mod.rs

@@ -72,6 +72,7 @@ pub use metrics::{
 
 /// The key type ID for a collator key.
 pub const COLLATOR_KEY_TYPE_ID: KeyTypeId = KeyTypeId(*b"coll");
+const LOG_TARGET: &str = "runtime::primitives";
 
 mod collator_app {
 	use application_crypto::{app_crypto, sr25519};
@@ -746,17 +747,29 @@ impl<H> BackedCandidate<H> {
 ///
 /// Returns either an error, indicating that one of the signatures was invalid or that the index
 /// was out-of-bounds, or the number of signatures checked.
-pub fn check_candidate_backing<H: AsRef<[u8]> + Clone + Encode>(
+pub fn check_candidate_backing<H: AsRef<[u8]> + Clone + Encode + core::fmt::Debug>(
 	backed: &BackedCandidate<H>,
 	signing_context: &SigningContext<H>,
 	group_len: usize,
 	validator_lookup: impl Fn(usize) -> Option<ValidatorId>,
 ) -> Result<usize, ()> {
 	if backed.validator_indices.len() != group_len {
+		log::debug!(
+			target: LOG_TARGET,
+			"Check candidate backing: indices mismatch: group_len = {} , indices_len = {}",
+			group_len,
+			backed.validator_indices.len(),
+		);
 		return Err(())
 	}
 
 	if backed.validity_votes.len() > group_len {
+		log::debug!(
+			target: LOG_TARGET,
+			"Check candidate backing: Too many votes, expected: {}, found: {}",
+			group_len,
+			backed.validity_votes.len(),
+		);
 		return Err(())
 	}
 
@@ -778,11 +791,23 @@ pub fn check_candidate_backing<H: AsRef<[u8]> + Clone + Encode>(
 		if sig.verify(&payload[..], &validator_id) {
 			signed += 1;
 		} else {
+			log::debug!(
+				target: LOG_TARGET,
+				"Check candidate backing: Invalid signature. validator_id = {:?}, validator_index = {} ",
+				validator_id,
+				val_in_group_idx,
+			);
 			return Err(())
 		}
 	}
 
 	if signed != backed.validity_votes.len() {
+		log::error!(
+			target: LOG_TARGET,
+			"Check candidate backing: Too many signatures, expected = {}, found = {}",
+			backed.validity_votes.len() ,
+			signed,
+		);
 		return Err(())
 	}
 

polkadot/primitives/src/vstaging/mod.rs

@@ -64,9 +64,13 @@ pub mod node_features {
 		/// Tells if tranch0 assignments could be sent in a single certificate.
 		/// Reserved for: `<https://github.com/paritytech/polkadot-sdk/issues/628>`
 		EnableAssignmentsV2 = 0,
+		/// This feature enables the extension of `BackedCandidate::validator_indices` by 8 bits.
+		/// The value stored there represents the assumed core index where the candidates
+		/// are backed. This is needed for the elastic scaling MVP.
+		ElasticScalingMVP = 1,
 		/// First unassigned feature bit.
 		/// Every time a new feature flag is assigned it should take this value.
 		/// and this should be incremented.
-		FirstUnassigned = 1,
+		FirstUnassigned = 2,
 	}
 }

polkadot/statement-table/Cargo.toml

@@ -13,3 +13,4 @@ workspace = true
 parity-scale-codec = { version = "3.6.1", default-features = false, features = ["derive"] }
 sp-core = { path = "../../substrate/primitives/core" }
 primitives = { package = "polkadot-primitives", path = "../primitives" }
+gum = { package = "tracing-gum", path = "../node/gum" }

polkadot/statement-table/src/generic.rs

@@ -36,6 +36,7 @@ use primitives::{
 };
 
 use parity_scale_codec::{Decode, Encode};
+const LOG_TARGET: &str = "parachain::statement-table";
 
 /// Context for the statement table.
 pub trait Context {
@@ -53,9 +54,6 @@ pub trait Context {
 	/// get the digest of a candidate.
 	fn candidate_digest(candidate: &Self::Candidate) -> Self::Digest;
 
-	/// get the group of a candidate.
-	fn candidate_group(candidate: &Self::Candidate) -> Self::GroupId;
-
 	/// Whether a authority is a member of a group.
 	/// Members are meant to submit candidates and vote on validity.
 	fn is_member_of(&self, authority: &Self::AuthorityId, group: &Self::GroupId) -> bool;
@@ -342,13 +340,13 @@ impl<Ctx: Context> Table<Ctx> {
 	pub fn import_statement(
 		&mut self,
 		context: &Ctx,
+		group_id: Ctx::GroupId,
 		statement: SignedStatement<Ctx::Candidate, Ctx::Digest, Ctx::AuthorityId, Ctx::Signature>,
 	) -> Option<Summary<Ctx::Digest, Ctx::GroupId>> {
 		let SignedStatement { statement, signature, sender: signer } = statement;
-
 		let res = match statement {
 			Statement::Seconded(candidate) =>
-				self.import_candidate(context, signer.clone(), candidate, signature),
+				self.import_candidate(context, signer.clone(), candidate, signature, group_id),
 			Statement::Valid(digest) =>
 				self.validity_vote(context, signer.clone(), digest, ValidityVote::Valid(signature)),
 		};
@@ -387,9 +385,10 @@ impl<Ctx: Context> Table<Ctx> {
 		authority: Ctx::AuthorityId,
 		candidate: Ctx::Candidate,
 		signature: Ctx::Signature,
+		group: Ctx::GroupId,
 	) -> ImportResult<Ctx> {
-		let group = Ctx::candidate_group(&candidate);
 		if !context.is_member_of(&authority, &group) {
+			gum::debug!(target: LOG_TARGET,  authority = ?authority, group = ?group, "New `Misbehavior::UnauthorizedStatement`, candidate backed by validator that doesn't belong to expected group" );
 			return Err(Misbehavior::UnauthorizedStatement(UnauthorizedStatement {
 				statement: SignedStatement {
 					signature,
@@ -634,10 +633,6 @@ mod tests {
 			Digest(candidate.1)
 		}
 
-		fn candidate_group(candidate: &Candidate) -> GroupId {
-			GroupId(candidate.0)
-		}
-
 		fn is_member_of(&self, authority: &AuthorityId, group: &GroupId) -> bool {
 			self.authorities.get(authority).map(|v| v == group).unwrap_or(false)
 		}
@@ -675,10 +670,10 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement_a);
+		table.import_statement(&context, GroupId(2), statement_a);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
-		table.import_statement(&context, statement_b);
+		table.import_statement(&context, GroupId(2), statement_b);
 		assert_eq!(
 			table.detected_misbehavior[&AuthorityId(1)][0],
 			Misbehavior::MultipleCandidates(MultipleCandidates {
@@ -711,10 +706,10 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement_a);
+		table.import_statement(&context, GroupId(2), statement_a);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
-		table.import_statement(&context, statement_b);
+		table.import_statement(&context, GroupId(2), statement_b);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 	}
 
@@ -735,7 +730,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement);
+		table.import_statement(&context, GroupId(2), statement);
 
 		assert_eq!(
 			table.detected_misbehavior[&AuthorityId(1)][0],
@@ -769,7 +764,7 @@ mod tests {
 		};
 		let candidate_a_digest = Digest(100);
 
-		table.import_statement(&context, candidate_a);
+		table.import_statement(&context, GroupId(2), candidate_a);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 
@@ -779,7 +774,7 @@ mod tests {
 			signature: Signature(2),
 			sender: AuthorityId(2),
 		};
-		table.import_statement(&context, bad_validity_vote);
+		table.import_statement(&context, GroupId(3), bad_validity_vote);
 
 		assert_eq!(
 			table.detected_misbehavior[&AuthorityId(2)][0],
@@ -811,7 +806,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, statement);
+		table.import_statement(&context, GroupId(2), statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let invalid_statement = SignedStatement {
@@ -820,7 +815,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, invalid_statement);
+		table.import_statement(&context, GroupId(2), invalid_statement);
 		assert!(table.detected_misbehavior.contains_key(&AuthorityId(1)));
 	}
 
@@ -842,7 +837,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement);
+		table.import_statement(&context, GroupId(2), statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let extra_vote = SignedStatement {
@@ -851,7 +846,7 @@ mod tests {
 			sender: AuthorityId(1),
 		};
 
-		table.import_statement(&context, extra_vote);
+		table.import_statement(&context, GroupId(2), extra_vote);
 		assert_eq!(
 			table.detected_misbehavior[&AuthorityId(1)][0],
 			Misbehavior::ValidityDoubleVote(ValidityDoubleVote::IssuedAndValidity(
@@ -910,7 +905,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement);
+		table.import_statement(&context, GroupId(2), statement);
 
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 		assert!(table.attested_candidate(&candidate_digest, &context, 2).is_none());
@@ -921,7 +916,7 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		table.import_statement(&context, vote);
+		table.import_statement(&context, GroupId(2), vote);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 		assert!(table.attested_candidate(&candidate_digest, &context, 2).is_some());
 	}
@@ -944,7 +939,7 @@ mod tests {
 		};
 
 		let summary = table
-			.import_statement(&context, statement)
+			.import_statement(&context, GroupId(2), statement)
 			.expect("candidate import to give summary");
 
 		assert_eq!(summary.candidate, Digest(100));
@@ -971,7 +966,7 @@ mod tests {
 		};
 		let candidate_digest = Digest(100);
 
-		table.import_statement(&context, statement);
+		table.import_statement(&context, GroupId(2), statement);
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(1)));
 
 		let vote = SignedStatement {
@@ -980,8 +975,9 @@ mod tests {
 			sender: AuthorityId(2),
 		};
 
-		let summary =
+		let summary = table
-			table.import_statement(&context, vote).expect("candidate vote to give summary");
+			.import_statement(&context, GroupId(2), vote)
+			.expect("candidate vote to give summary");
 
 		assert!(!table.detected_misbehavior.contains_key(&AuthorityId(2)));
 

polkadot/statement-table/src/lib.rs

@@ -35,8 +35,8 @@ pub use generic::{Config, Context, Table};
 pub mod v2 {
 	use crate::generic;
 	use primitives::{
-		CandidateHash, CommittedCandidateReceipt, CompactStatement as PrimitiveStatement, Id,
+		CandidateHash, CommittedCandidateReceipt, CompactStatement as PrimitiveStatement,
-		ValidatorIndex, ValidatorSignature,
+		CoreIndex, ValidatorIndex, ValidatorSignature,
 	};
 
 	/// Statements about candidates on the network.
@@ -59,7 +59,7 @@ pub mod v2 {
 	>;
 
 	/// A summary of import of a statement.
-	pub type Summary = generic::Summary<CandidateHash, Id>;
+	pub type Summary = generic::Summary<CandidateHash, CoreIndex>;
 
 	impl<'a> From<&'a Statement> for PrimitiveStatement {
 		fn from(s: &'a Statement) -> PrimitiveStatement {