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rust: dma: remove DMA_ATTR_NO_KERNEL_MAPPING from public attrs

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>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260321172749.592387-1-dakr@kernel.org
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

authored by

Danilo Krummrich and committed by
Alexandre Courbot 18fb5f1f 15a4bb87

-3
-3
rust/kernel/dma.rs
··· 267 267 /// Specifies that writes to the mapping may be buffered to improve performance. 268 268 pub const DMA_ATTR_WRITE_COMBINE: Attrs = Attrs(bindings::DMA_ATTR_WRITE_COMBINE); 269 269 270 - /// Lets the platform to avoid creating a kernel virtual mapping for the allocated buffer. 271 - pub const DMA_ATTR_NO_KERNEL_MAPPING: Attrs = Attrs(bindings::DMA_ATTR_NO_KERNEL_MAPPING); 272 - 273 270 /// Allows platform code to skip synchronization of the CPU cache for the given buffer assuming 274 271 /// that it has been already transferred to 'device' domain. 275 272 pub const DMA_ATTR_SKIP_CPU_SYNC: Attrs = Attrs(bindings::DMA_ATTR_SKIP_CPU_SYNC);