Re: [PATCH 1/2] rust: dma: remove DMA_ATTR_NO_KERNEL_MAPPING from public attrs

[Alexandre Courbot]

On Sun Mar 22, 2026 at 2:27 AM JST, Danilo Krummrich wrote:
> When DMA_ATTR_NO_KERNEL_MAPPING is passed to dma_alloc_attrs(), the
> returned CPU address is not a pointer to the allocated memory but an
> opaque handle (e.g. struct page *).
>
> Coherent<T> (or CoherentAllocation<T> respectively) stores this value as
> NonNull<T> and exposes methods that dereference it and even modify its
> contents.
>
> Remove the flag from the public attrs module such that drivers cannot
> pass it to Coherent<T> (or CoherentAllocation<T> respectively) in the
> first place.
>
> Instead DMA_ATTR_NO_KERNEL_MAPPING can be supported with an additional
> opaque type (e.g. CoherentHandle) which does not provide access to the
> allocated memory.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>

Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>