Re: [PATCH v3] rust: page: add byte-wise atomic memory copy methods

[Andreas Hindborg]

Boqun Feng <boqun@xxxxxxxxxx> writes:

> On Fri, Feb 13, 2026 at 07:42:53AM +0100, Andreas Hindborg wrote:
> [...]
>> diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
>> index 4aebeacb961a2..8ab20126a88cf 100644
>> --- a/rust/kernel/sync/atomic.rs
>> +++ b/rust/kernel/sync/atomic.rs
>> @@ -560,3 +560,35 @@ pub fn fetch_add<Rhs, Ordering: ordering::Ordering>(&self, v: Rhs, _: Ordering)
>>          unsafe { from_repr(ret) }
>>      }
>>  }
>> +
>> +/// Copy `len` bytes from `src` to `dst` using byte-wise atomic operations.
>> +///
>
> Given Greg and Peter's feedback, I think it's better to call out why we
> need `atomic_per_byte_memcpy()` and why we use bindings::memcpy() to
> implement it. How about a paragraph as follow:
>
> /// This is the concurrent-safe version of `core::ptr::copy()` (the
> /// counterpart of standard C's `memcpy()`). Because of the atomicity at
> /// byte level, when racing with another concurrent atomic access (or
> /// a normal read races with an atomic read) or an external access (from
> /// DMA or userspace), the behavior of this function is defined:
> /// copying memory at the (at least) byte granularity.
> ///
> /// Implementation note: it's currently implemented by kernel's
> /// `memcpy()`, because kernel's `memcpy()` is implemented in a way that
> /// byte-wise atomic memory load/store instructions are used.
>
> And probably we make it a separate patch for this
> atomic_per_byte_memcpy().

Sure, I'll queue that.


Best regards,
Andreas Hindborg