Re: [PATCH v3] gpu: nova-core: gsp: fix undefined behavior in command queue code

[Danilo Krummrich]

On Thu Mar 26, 2026 at 6:43 AM CET, Alexandre Courbot wrote:
> +        // - Since `data` was created from a valid pointer, both `tail_slice` and `wrap_slice` are
> +        //   pointers to valid arrays.
> +        // - The area starting at `tx` and ending at `rx - 2` modulo `MSGQ_NUM_PAGES`,
> +        //   inclusive, belongs to the driver for writing and is not accessed concurrently by
> +        //   the GSP.
> +        // - The caller holds a reference to `self` for as long as the returned slices are live,
> +        //   meaning the CPU write pointer cannot be advanced and thus that the returned area
> +        //   remains exclusive to the CPU for the duration of the slices.
> +        (unsafe { &mut *tail_slice }, unsafe { &mut *wrap_slice })

I think this does miss the justification for tail_slice and wrap_slice to not
overlap, i.e. don't we need something like:

	- `tail_slice` and `wrap_slice` point to non-overlapping sub-ranges of `data` in all
	  branches (in the `rx <= tx` case, `wrap_slice` ends at `rx - 1` which is strictly less
	  than `tx` where `tail_slice` starts; in the other cases one of the slices is empty),
	  so creating two `&mut` references from them does not violate aliasing rules.

With this considered,

Reviewed-by: Danilo Krummrich <dakr@xxxxxxxxxx>