The instructions for line 19 (passive activities) of Form 6251 (Alternative Minimum Tax) mention that you may need to do an AMT version of Form 8582 (Passive Activity Loss Limitations):
Refigure your passive activity gains and losses for the AMT by taking into account all adjustments and preferences and any AMT prior year unallowed losses that apply to that activity. You may fill out an AMT Form 8582, Passive Activity Loss Limitations, and AMT versions of the other forms or schedules on which your passive activities are reported, to determine your passive activity loss allowed for the AMT, but don’t file the AMT versions of these forms and schedules with your tax return. Instead, keep them with your records.
However, when you look at the instructions for Part II, line 7 of Form 8582, there's no direction for how to calculate your AMT MAGI, only your regular MAGI.
TurboTax seemed to just take my regular MAGI and subtract my state income tax refund. However, I deducted state income tax on Schedule A, and it seems odd that my state income tax refund would be subtracted to yield my AMT MAGI, but my state income tax deduction would not get added back in. Is there any authority for how to calculate your AMT MAGI for passive activity loss limitations?