I am familiar more with VA laws than TN laws. Here is what I have found out.
VA -- There is no length law in VA. (Some cities may have instituted stricter ordinances.) It is however, illegal to
conceal a dirk, dagger, bowie, or "like weapon". Basically that means you may carry openly any straight bladed knife no matter the size for legal purposes.
Be aware that pushing the size of your blade will increase your chances of being stopped and questioned. A police officer would wonder and probably question a person walking down the street with a 2 foot long machete or sword.
TN -- (Again, be aware I can only speculate by what I read. I only have access to the TN code, and not case law.) It seems that the only thing you can't carry knife wise is a switchblade. It is however, illegal to "carry with the intent to go armed" any knife over 4.5 inches. That would seem to indicate that if you could have a reason to carry a knife that is larger for a valid tool use (ie. hunting) it would be okay.
I suggest you call the State Attorney Generals Offices in both states. They should be able to give you a clear understanding of what you need. here is a link:
http://akti.org/legislation.asp?n=47
BTW Conceal carry permits in both states are handgun only permits.
Pam