Re: [PATCH] rust: page: add volatile memory copy methods

[Boqun Feng <boqun@kernel.org>]

On Sat, Jan 31, 2026 at 02:19:05PM +0100, Andreas Hindborg wrote:
[..]
> >
> > However, byte-wise atomic memcpy will be more defined without paying any
> > extra penalty.
> 
> Could you explain the additional penalty of `core::ptr::read_volatile`
> vs `kernel::sync::atomic::Atomic::load` with  relaxed ordering?
> 

I don't understand your question, so allow me to explain what I meant:
for the sake of discussion, let's assume we have both

	fn volatile_copy_memory(src: *mut u8, dst: *mut u8, count: usize)

and

	fn volatile_byte_wise_atomic_copy_memory(<same signature>, ordering: Ordering)

implemented. What I meant was to the best of my knowledge, when ordering
= Relaxed, these two would generate the exact same code because all the
architectures that I'm aware of have byte wise atomicity in the
load/store instructions. And compared to volatile_copy_memory(),
volatile_byte_wise_atomic_copy_memory() can bear the race with another
volatile_byte_wise_atomic_copy_memory() or any other atomic access
(meaning that's not a UB). So I'd prefer using that if we have it.

Regards,
Boqun

> 
> Best regards,
> Andreas Hindborg
> 
>