There are no magazine restrictions. If a magazine can hold more than 20 rounds the state of Virginia considers it and "assault weapon" and the person must comply with Virginia's "assault weapons" laws.
Some states have a limit on the number of rounds a magazine can hold. In these states purchasing, selling, or transferring a magazine of larger size than the law allows is a crime. In some cases magazines that were bought before the law was put in place must be registered with the police, in others they may only be loaded to the number of rounds legal in a state. The law may vary in some cities.