[coyotos-dev] GPT questions

[Charles Landau]

1. If my understanding is correct, in a window capability, the guard 
and the offset are redundant. The offset is added to the virtual 
address, and the guard is effectively subtracted.

I can understand why you might want both. The offset has more bits, 
and the logic might be simpler if you allow guards in window keys as 
well as other memory keys that don't contain an offset.

2. At http://www.coyotos.org/docs/ukernel/spec.html#as_compose, the 
spec says "Care should be taken to set the l2v value appropriately 
when the ha [or bg] bit is set. " Do you mean that l2v should be >= 
61, so there is no possibility of using slots 14 and 15 in 
translation (because u < 8)? Or simply that the u field of the 
address space should be no more than 3 bits in size, which happens if 
l2v is at least 3 + the *expected* value of l2g? In the latter case, 
the GPT can't be sure that someone won't create a new capability to 
the GPT with a different l2g.