[DESIGN] updateManaTarget Only Allows Increases, Not Decreases

[evmparser]

Summary

The updateManaTarget function in RollupCore.sol only allows the mana target to be increased, never decreased, which may be overly restrictive for network management.

Severity

LOW - Design consideration, not a bug

Location

• File: l1-contracts/src/core/RollupCore.sol
• Function: updateManaTarget

Description

The function enforces a one-way restriction:

function updateManaTarget(uint256 _manaTarget) external override(IRollupCore) onlyOwner {
    uint256 currentManaTarget = FeeLib.getStorage().config.getManaTarget();
    require(_manaTarget >= currentManaTarget, Errors.Rollup__InvalidManaTarget(_manaTarget, currentManaTarget));
    // ...
}

Current Behavior

• Mana target can only be increased
• Any attempt to decrease it will revert
• Comment states: "We only allow increasing the mana target to avoid governance killing an old rollup"

Potential Issues

1. Limited Flexibility: Network conditions may require lowering the mana target
2. Economic Adjustments: Market changes might necessitate target reduction
3. Emergency Response: Unable to quickly adjust downward in crisis scenarios
4. Upgrade Required: Decreasing target requires full contract upgrade

Impact

• Governance lacks flexibility to respond to changing network conditions
• May force unnecessary contract upgrades for parameter adjustments
• Could lead to suboptimal network performance if target becomes too high

Discussion Points

Arguments for current design:

• Prevents malicious governance from "killing" the rollup
• Provides stability and predictability
• Protects against governance attacks

Arguments for allowing decreases:

• Governance should have full control over network parameters
• Other safeguards (timelock, multi-sig) can prevent abuse
• Network conditions may genuinely require lower targets
• Could add a minimum threshold instead of one-way restriction

Recommendation

Consider one of these approaches:

Option 1: Allow both increases and decreases with a minimum threshold:

uint256 constant MIN_MANA_TARGET = 1000; // Define reasonable minimum
require(_manaTarget >= MIN_MANA_TARGET, "Below minimum mana target");

Option 2: Add a separate "emergency decrease" function with stricter controls

Option 3: Keep current design but document the rationale clearly

Request

Please clarify if this one-way restriction is intentional and desired long-term, or if more flexibility should be considered for future versions.