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

["Gary Guo" <gary@garyguo.net>]

On Thu Mar 26, 2026 at 5:43 AM GMT, Alexandre Courbot wrote:
> `driver_read_area` and `driver_write_area` are internal methods that
> return slices containing the area of the command queue buffer that the
> driver has exclusive read or write access, respectively.
> 
> While their returned value is correct and safe to use, internally they
> temporarily create a reference to the whole command-buffer slice,
> including GSP-owned regions. These regions can change without notice,
> and thus creating a slice to them, even if never accessed, is undefined
> behavior.
> 
> Fix this by rewriting these methods to use pointer projections in order
> to create slices to valid regions only. It should eventually be replaced
> by `IoView` and `IoSlice` once they land.
> 
> Fixes: 75f6b1de8133 ("gpu: nova-core: gsp: Add GSP command queue bindings and handling")
> Reported-by: Danilo Krummrich <dakr@kernel.org>
> Closes: https://lore.kernel.org/all/DH47AVPEKN06.3BERUSJIB4M1R@kernel.org/
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

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

> ---
> Changes in v3:
> - Rebase on top of latest `drm-rust-next` (with `Coherent` patches).
> - Use pointer projections. (thanks Gary!)
> - Link to v2: https://patch.msgid.link/20260323-cmdq-ub-fix-v2-1-77d1213c3f7f@nvidia.com
> 
> Changes in v2:
> - Use `u32_as_usize` consistently.
> - Reduce the number of `unsafe` blocks by computing the end offset of
>   the returned slices and creating them at the end, in one step.
> - Take advantage of the fact that both slices have the same start index
>   regardless of the branch chosen.
> - Improve safety comments.
> - Link to v1: https://patch.msgid.link/20260319-cmdq-ub-fix-v1-1-0f9f6e8f3ce3@nvidia.com
> ---
>  drivers/gpu/nova-core/gsp/cmdq.rs | 104 ++++++++++++++++++++------------------
>  1 file changed, 55 insertions(+), 49 deletions(-)