RE: [PATCH v3 2/2] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc()

[David Laight]

From: David Howells
> Sent: Wednesday, August 16, 2023 1:08 PM

Given:

> iter->copy_mc is only used with a bvec iterator and only by
> dump_emit_page() in fs/coredump.c so rather than handle this in
> memcpy_from_iter_mc() where it is checked repeatedly by _copy_from_iter() and
> copy_page_from_iter_atomic(),

Instead of adding the extra check to every copy:

> +static __always_inline
> +size_t __copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
> +{
> +	if (unlikely(iov_iter_is_copy_mc(i)))
> +		return __copy_from_iter_mc(addr, bytes, i);
> +	return iterate_and_advance(i, bytes, addr,
> +				   copy_from_user_iter, memcpy_from_iter);
>  }

Couldn't the relevant code directly call __copy_frtom_iter_mc() ?
Or a version then checked iov_is_copy_mc() and then fell
back to the standard function.

	David

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