Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v4 02/24] powerpc/pseries: Fix alignment of PLPKS structures and buffers | Date | Fri, 27 Jan 2023 21:52:31 +1100 |
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Segher Boessenkool <segher@kernel.crashing.org> writes: > On Thu, Jan 26, 2023 at 12:09:53AM +1100, Michael Ellerman wrote: >> Andrew Donnellan <ajd@linux.ibm.com> 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
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