Socialist/Communism pacifism is the view socialism or communism condems all violence, since true anarchism is communist, anarcho-pacifism is a type of this ideology. An socialist-pacifist party is the PFP(California).
Of course, Mao, Lenin, Stalin and Ho Chin Mo fought and/or commanded in a war and therefore many socialist and communist pacifists don't share their ideologies or don't state it.
I believe that war should be very limited, and communism does support it because most wars are the profit of few, the powerful. However, if the powerful few attack you PHYISCIALLY you have some violence(wheter or not it goes to outright killing) to defend yourself.
Therefore, straightout pacifism is contradictary with Orthodox Marxism but you don't believe wars should be limited, you can't be a communist or a socialist.