Re: [PATCH 4/4] rust: dma: tie Coherent and CoherentBox to the device's bound lifetime

[Gary Guo]

On Sun Aug 30, 2026 at 8:37 PM BST, Danilo Krummrich wrote:
> Add a lifetime parameter to Coherent and CoherentBox that ties the DMA
> allocation to the device's bound scope, ensuring it is freed before the
> device is unbound.
> 
> DMA allocations carry device resources (e.g. IOMMU mappings) that must
> not outlive the device's bound lifetime. Without a lifetime parameter,
> there was no compile-time enforcement that a Coherent or CoherentBox is
> dropped before the device is unbound.
> 
> Propagate the new lifetime parameter through all users.
> 
> Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>

The rust/kernel code looks good to me. Haven't checked nova part in detail, but
it looks like a mechanical conversion, so would be fine if it builds.

Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

Sashiko points out that the `Coherent` could be leaked -- what's the implication
when that happens? I think it's not going to be as problematic like
registrations because coherent allocation carries no callbacks, so we probably
don't need this to be unsafe, but I do wonder how'd DMA subsystem handle this.

Best,
Gary

> ---
>  drivers/gpu/nova-core/falcon.rs               |   2 +-
>  drivers/gpu/nova-core/fb.rs                   |   2 +-
>  drivers/gpu/nova-core/firmware/booter.rs      |   2 +-
>  drivers/gpu/nova-core/firmware/fsp.rs         |   8 +-
>  .../nova-core/firmware/fwsec/bootloader.rs    |  12 +-
>  drivers/gpu/nova-core/firmware/gsp.rs         |  14 +-
>  drivers/gpu/nova-core/firmware/riscv.rs       |   8 +-
>  drivers/gpu/nova-core/fsp.rs                  |  20 +--
>  drivers/gpu/nova-core/gpu.rs                  |   4 +-
>  drivers/gpu/nova-core/gsp.rs                  |  30 ++---
>  drivers/gpu/nova-core/gsp/boot.rs             |  10 +-
>  drivers/gpu/nova-core/gsp/cmdq.rs             |  35 +++--
>  drivers/gpu/nova-core/gsp/commands.rs         |   2 +-
>  drivers/gpu/nova-core/gsp/fw.rs               |  12 +-
>  drivers/gpu/nova-core/gsp/hal.rs              |  14 +-
>  drivers/gpu/nova-core/gsp/hal/gh100.rs        |  16 +--
>  drivers/gpu/nova-core/gsp/hal/tu102.rs        |  34 ++---
>  drivers/gpu/nova-core/gsp/sequencer.rs        |   6 +-
>  rust/kernel/dma.rs                            | 121 +++++++++---------
>  rust/kernel/uaccess.rs                        |   4 +-
>  samples/rust/rust_dma.rs                      |   4 +-
>  21 files changed, 176 insertions(+), 184 deletions(-)