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

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

[Danilo Krummrich]

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@vger.kernel.org
Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/dma.rs | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 6d2bec52806b..9e0c9ff91cba 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -264,9 +264,6 @@ pub mod attrs {
     /// Specifies that writes to the mapping may be buffered to improve performance.
     pub const DMA_ATTR_WRITE_COMBINE: Attrs = Attrs(bindings::DMA_ATTR_WRITE_COMBINE);
 
-    /// Lets the platform to avoid creating a kernel virtual mapping for the allocated buffer.
-    pub const DMA_ATTR_NO_KERNEL_MAPPING: Attrs = Attrs(bindings::DMA_ATTR_NO_KERNEL_MAPPING);
-
     /// Allows platform code to skip synchronization of the CPU cache for the given buffer assuming
     /// that it has been already transferred to 'device' domain.
     pub const DMA_ATTR_SKIP_CPU_SYNC: Attrs = Attrs(bindings::DMA_ATTR_SKIP_CPU_SYNC);
-- 
2.53.0

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

[Gary Guo]

On Sat Mar 21, 2026 at 5:27 PM GMT, 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@vger.kernel.org
> Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/dma.rs | 3 ---
>  1 file changed, 3 deletions(-)

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

[Alice Ryhl]

On Sat, Mar 21, 2026 at 6:27 PM Danilo Krummrich <dakr@kernel.org> 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@vger.kernel.org
> Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

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@vger.kernel.org
> Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>