The only book I have read that dealt with the Soviet Afghan War is The Global Cold War; Third World Interventions and the Making of Our Times, by Odd Arne Westad. Just one chapter of the book focuses on the war but it is an illuminating study with a good argument I think. I don't think Westad considers himself a Marxist per say but I think his anti-imperialist, anti-Western chauvinist outlook is acceptable for Marxists.