Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> writes: > On Thu, Jan 26, 2023 at 12:09:53AM +1100, Michael Ellerman wrote: >> Andrew Donnellan <ajd@xxxxxxxxxxxxx> writes: >> > A number of structures and buffers passed to PKS hcalls have alignment >> > requirements, which could on occasion cause problems: >> > >> > - Authorisation structures must be 16-byte aligned and must not cross a >> > page boundary >> > >> > - Label structures must not cross page boundaries >> > >> > - Password output buffers must not cross page boundaries >> > >> > Round up the allocations of these structures/buffers to the next power of >> > 2 to make sure this happens. >> >> It's not the *next* power of 2, it's the *nearest* power of 2, including >> the initial value if it's already a power of 2. > > It's not the nearest either, the nearest power of two to 65 is 64. You > could say "but, round up" to which I would say "round?" :-P OK you got me there :) The function name makes it pretty clear that it will round *up* to the nearest power of 2 but you're right the comment should also make that clear. > "Adjust the allocation size to be the smallest power of two greater than > or equal to the given size." > > "Pad to a power of two" in shorthand. "Padded to a power of two if > necessary" if you want to emphasise it can be a no-op. The initial wording implied that it would always over-allocate so yes I think it's important to make it clear that it doesn't round up if it doesn't need to. cheers
