Plot3D[{1+Sqrt[4-(x-1)^2-(y+1)^2],1-Sqrt[4-(x-1)^2-(y+1)^2]},{x,1-2,1+2},{y,-1-2,0},RegionFunction->Function[{x,y,z},(x-1)^2+(y+1)^2≤4],BoxRatios->Automatic,Axes->True]

Graphics3D[Cylinder[{{1,-1,-1},{1,-1,1}},2],Axes->True]