Restrict ProposerVM P-chain height advancement (#3777)

Signed-off-by: Stephen Buttolph <stephen@avalabs.org>
Co-authored-by: Arran Schlosberg <519948+ARR4N@users.noreply.github.com>

Author: StephenButtolph

vms/proposervm/block.go

@@ -193,7 +193,7 @@ func (p *postForkCommonComponents) buildChild(
 
 	// The child's P-Chain height is proposed as the optimal P-Chain height that
 	// is at least the parent's P-Chain height
-	pChainHeight, err := p.vm.optimalPChainHeight(ctx, parentPChainHeight)
+	pChainHeight, err := p.vm.selectChildPChainHeight(ctx, parentPChainHeight)
 	if err != nil {
 		p.vm.ctx.Log.Error("unexpected build block failure",
 			zap.String("reason", "failed to calculate optimal P-chain height"),

vms/proposervm/pre_fork_block.go

@@ -192,7 +192,7 @@ func (b *preForkBlock) buildChild(ctx context.Context) (Block, error) {
 
 	// The child's P-Chain height is proposed as the optimal P-Chain height that
 	// is at least the minimum height
-	pChainHeight, err := b.vm.optimalPChainHeight(ctx, b.vm.Upgrades.ApricotPhase4MinPChainHeight)
+	pChainHeight, err := b.vm.selectChildPChainHeight(ctx, b.vm.Upgrades.ApricotPhase4MinPChainHeight)
 	if err != nil {
 		b.vm.ctx.Log.Error("unexpected build block failure",
 			zap.String("reason", "failed to calculate optimal P-chain height"),

vms/proposervm/vm.go

@@ -725,13 +725,31 @@ func (vm *VM) notifyInnerBlockReady() {
 	}
 }
 
-func (vm *VM) optimalPChainHeight(ctx context.Context, minPChainHeight uint64) (uint64, error) {
-	minimumHeight, err := vm.ctx.ValidatorState.GetMinimumHeight(ctx)
+// fujiOverridePChainHeightUntilHeight is the P-chain height at which the
+// proposervm will no longer attempt to keep the P-chain height the same.
+const fujiOverridePChainHeightUntilHeight = 200041
+
+// fujiOverridePChainHeightUntilTimestamp is the timestamp at which the
+// proposervm will no longer attempt to keep the P-chain height the same.
+var fujiOverridePChainHeightUntilTimestamp = time.Date(2025, time.March, 7, 17, 0, 0, 0, time.UTC) // noon ET
+
+func (vm *VM) selectChildPChainHeight(ctx context.Context, minPChainHeight uint64) (uint64, error) {
+	var (
+		now            = vm.Clock.Time()
+		shouldOverride = vm.ctx.NetworkID == constants.FujiID &&
+			vm.ctx.SubnetID != constants.PrimaryNetworkID &&
+			now.Before(fujiOverridePChainHeightUntilTimestamp) &&
+			minPChainHeight < fujiOverridePChainHeightUntilHeight
+	)
+	if shouldOverride {
+		return minPChainHeight, nil
+	}
+
+	recommendedHeight, err := vm.ctx.ValidatorState.GetMinimumHeight(ctx)
 	if err != nil {
 		return 0, err
 	}
-
-	return max(minimumHeight, minPChainHeight), nil
+	return max(recommendedHeight, minPChainHeight), nil
 }
 
 // parseInnerBlock attempts to parse the provided bytes as an inner block. If

vms/proposervm/vm_test.go

@@ -37,6 +37,7 @@ import (
 	"github.com/ava-labs/avalanchego/upgrade"
 	"github.com/ava-labs/avalanchego/upgrade/upgradetest"
 	"github.com/ava-labs/avalanchego/utils"
+	"github.com/ava-labs/avalanchego/utils/constants"
 	"github.com/ava-labs/avalanchego/utils/logging"
 	"github.com/ava-labs/avalanchego/utils/timer/mockable"
 	"github.com/ava-labs/avalanchego/vms/proposervm/proposer"
@@ -2571,3 +2572,91 @@ func TestTimestampMetrics(t *testing.T) {
 		})
 	}
 }
+
+func TestSelectChildPChainHeight(t *testing.T) {
+	var (
+		activationTime = time.Unix(0, 0)
+		durangoTime    = activationTime
+
+		beforeOverrideEnds = fujiOverridePChainHeightUntilTimestamp.Add(-time.Minute)
+	)
+	for _, test := range []struct {
+		name                 string
+		time                 time.Time
+		networkID            uint32
+		subnetID             ids.ID
+		currentPChainHeight  uint64
+		minPChainHeight      uint64
+		expectedPChainHeight uint64
+	}{
+		{
+			name:                 "no override - mainnet",
+			time:                 beforeOverrideEnds,
+			networkID:            constants.MainnetID,
+			subnetID:             ids.GenerateTestID(),
+			currentPChainHeight:  fujiOverridePChainHeightUntilHeight + 2,
+			minPChainHeight:      fujiOverridePChainHeightUntilHeight - 5,
+			expectedPChainHeight: fujiOverridePChainHeightUntilHeight + 2,
+		},
+		{
+			name:                 "no override - primary network",
+			time:                 beforeOverrideEnds,
+			networkID:            constants.FujiID,
+			subnetID:             constants.PrimaryNetworkID,
+			currentPChainHeight:  fujiOverridePChainHeightUntilHeight + 2,
+			minPChainHeight:      fujiOverridePChainHeightUntilHeight - 5,
+			expectedPChainHeight: fujiOverridePChainHeightUntilHeight + 2,
+		},
+		{
+			name:                 "no override - expired network",
+			time:                 fujiOverridePChainHeightUntilTimestamp,
+			networkID:            constants.FujiID,
+			subnetID:             ids.GenerateTestID(),
+			currentPChainHeight:  fujiOverridePChainHeightUntilHeight + 2,
+			minPChainHeight:      fujiOverridePChainHeightUntilHeight - 5,
+			expectedPChainHeight: fujiOverridePChainHeightUntilHeight + 2,
+		},
+		{
+			name:                 "no override - chain previously advanced",
+			time:                 beforeOverrideEnds,
+			networkID:            constants.FujiID,
+			subnetID:             ids.GenerateTestID(),
+			currentPChainHeight:  fujiOverridePChainHeightUntilHeight + 2,
+			minPChainHeight:      fujiOverridePChainHeightUntilHeight + 1,
+			expectedPChainHeight: fujiOverridePChainHeightUntilHeight + 2,
+		},
+		{
+			name:                 "override",
+			time:                 beforeOverrideEnds,
+			networkID:            constants.FujiID,
+			subnetID:             ids.GenerateTestID(),
+			currentPChainHeight:  fujiOverridePChainHeightUntilHeight + 2,
+			minPChainHeight:      fujiOverridePChainHeightUntilHeight - 5,
+			expectedPChainHeight: fujiOverridePChainHeightUntilHeight - 5,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			require := require.New(t)
+
+			_, vdrState, proVM, _ := initTestProposerVM(t, activationTime, durangoTime, 0)
+			defer func() {
+				require.NoError(proVM.Shutdown(context.Background()))
+			}()
+
+			proVM.Clock.Set(test.time)
+			proVM.ctx.NetworkID = test.networkID
+			proVM.ctx.SubnetID = test.subnetID
+
+			vdrState.GetMinimumHeightF = func(context.Context) (uint64, error) {
+				return test.currentPChainHeight, nil
+			}
+
+			actualPChainHeight, err := proVM.selectChildPChainHeight(
+				context.Background(),
+				test.minPChainHeight,
+			)
+			require.NoError(err)
+			require.Equal(test.expectedPChainHeight, actualPChainHeight)
+		})
+	}
+}