Re: [PATCH 3/7] maccess: Skip setup for zero-sized kernel nofault copies

> A zero-sized kernel nofault copy does not enter an access loop, but it
> still disables and re-enables page faults.
>
> Zero sizes are valid. BPF probe-read helpers accept them, and KGDB memory
> packets may carry a zero length.
>
> Return before changing page-fault state when there is nothing to copy.
> For reads, keep architecture-specific address validation before the fast
> path so its behavior is unchanged.

This isn't a bug, but would it help to say in the changelog that a later
patch in the series wraps these loops in a bare nofault (TCO) region and
relies on the operation never being empty, rather than framing this purely
as skipping the page-fault state change?

The current description focuses on the mechanical effect (skip
pagefault_disable/enable when there is nothing to copy), but on its own the
change appears to be a no-op: pagefault_disable and pagefault_enable only
increment and decrement current->pagefault_disabled, so a zero-size copy
already returned 0 without touching memory.


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