linux-kernel - Re: [PATCH 3/3] rust: dma: add as_slice/write functions for CoherentAllocation

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Message-Id: <D92V7PTBE3YP.2RFJGJS619NZN@nvidia.com>
Date: Thu, 10 Apr 2025 18:52:34 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Abdiel Janulgue" <abdiel.janulgue@...il.com>, <a.hindborg@...nel.org>,
 <ojeda@...nel.org>
Cc: "Danilo Krummrich" <dakr@...nel.org>, "Daniel Almeida"
 <daniel.almeida@...labora.com>, "Robin Murphy" <robin.murphy@....com>,
 "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>,
 "Gary Guo" <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <benno.lossin@...ton.me>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "open
 list:DMA MAPPING HELPERS DEVICE DRIVER API [RUST]"
 <rust-for-linux@...r.kernel.org>, "Marek Szyprowski"
 <m.szyprowski@...sung.com>, "open list:DMA MAPPING HELPERS"
 <iommu@...ts.linux.dev>, "open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] rust: dma: add as_slice/write functions for
 CoherentAllocation

On Thu Apr 10, 2025 at 6:02 PM JST, Abdiel Janulgue wrote:
> Hi Alex,
>
> On 08/04/2025 06:08, Alexandre Courbot wrote:
>>> +        }
>>> +        // SAFETY:
>>> +        // - The pointer is valid due to type invariant on `CoherentAllocation`
>>> +        // and we've just checked that the range and index is within bounds.
>>> +        // - `offset` can't overflow since it is smaller than `self.count` and we've checked
>>> +        // that `self.count` won't overflow early in the constructor.
>>> +        unsafe {
>>> +            core::ptr::copy_nonoverlapping(src.as_ptr(), self.cpu_addr.add(offset), src.len())
>>> +        };
>> 
>> How about leveraging as_slice_mut() so this unsafe block can be removed?
>
> as_slice_mut is still unsafe, no? So we couldn't remove unsafe block still?

Ah, that's right. In that case it would at least factorize the bound
check and make the method a bit shorter, unless I missed something else.