"such a smile as would have become the face of Malvolio"

Malvolio is Olivia’s deluded and much-mocked steward in Shakespeare’s Twelfth Night.  The reference is to Act 3 Scene 4:

 

Malvolio courts Olivia, while Maria watches in amusement
Public DomainMalvolio courts Olivia, while Maria watches in amusement - Credit: wikimedia commons
OLIVIA  

Where is Malvolio?

MARIA     

He's coming, madam; but in very strange manner. He
is, sure, possessed, madam.

OLIVIA     

Why, what's the matter? does he rave?

MARIA     

No. madam, he does nothing but smile: your
ladyship were best to have some guard about you, if
he come; for, sure, the man is tainted in's wits.

Read the whole scene here