On 04.01.23 23:52, Peter Xu wrote:
Switch to use type "long" for page accountings and retval across the whole
procedure of change_protection().
The change should have shrinked the possible maximum page number to be half
comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on any
system either because the maximum possible pages touched by change
protection should be ULONG_MAX / PAGE_SIZE.
Yeah, highly unlikely.
Two reasons to switch from "unsigned long" to "long":
1. It suites better on count_vm_numa_events(), whose 2nd parameter takes
a long type.
2. It paves way for returning negative (error) values in the future.
Currently the only caller that consumes this retval is change_prot_numa(),
where the unsigned long was converted to an int. Since at it, touching up
the numa code to also take a long, so it'll avoid any possible overflow too
during the int-size convertion.
I'm wondering if we should just return the number of changed pages via a
separate pointer and later using an int for returning errors -- when
touching this interface already.
Only who's actually interested in the number of pages would pass a
pointer to an unsigned long (NUMA).
And code that expects that there never ever are failures (mprotect,
NUMA) could simply check for WARN_ON_ONCE(ret).
I assume you evaluated that option as well, what was your conclusion?
--
Thanks,
David / dhildenb
