We're feeding essentially all of it - out of a world population of over 7,000,000,000, about 400,000 die of malnutrition per year. World food production per person is as high as it's ever been, over 2700 calories per person per day(which is really not a starvation diet). The ones who aren't getting fed are dying for logistical, financial, and administrative reasons, not because there's any sort of global food shortage.