Voldemort must know about Snape

[Deb]

No: HPFGUIDX 73728

At the end of PS, Quirrel tells Harry that it was Snape who saved
Harry's life, and that Snape was suspicious of Quirrel.  So, doesn't
this mean Voldemort knows where Snape's loyalties lie?  Any
explainations for this? How can he be a spy while Voldemort knows what
he has been up to? 

(I am assuming that Snape is on Dumbledore's side)

Deb S, aka readzalot, Canada