So I scanned through the various implementations, and I note:

m68k, arm32: Fixed.
mips, pc532: Looks right to me.
i386: I sent a patch to fvdl.
alpha: Saves pcb_onfault, but doesn't restore it after a fault.
powerpc, sparc, sparc64, vax: Broken.

As if for amusement value, the powerpc version even has a comment
above it mentioning that it needs to save pcb_onfault, but then
doesn't.