[PATCH v4 0/3] rust: add pointer projection infrastructure and convert DMA

[Gary Guo <gary@kernel.org>]

From: Gary Guo <gary@garyguo.net>

This adds a general pointer projection infrastructure which is intended to
serve as the basis for generic I/O projections. The idea is that we will
have a unified way of reading/writing MMIO or DMA allocation, creating
typed subviews into them, and able to read/write subfields safely.

This is the first step towards that direction, where an infra for
projecting arbitrary pointers are added. This takes care to not assume
pointers are part of a valid allocation, so it can be used to project I/O
pointers, too. `dma_read!` and `dma_write!` is converted to use this infra,
as they currently have soundness issues [1] and users have already
encountered limitation of it [2].

Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Soundness.20of.20.60dma_read!.28.29.60/with/573645610 [1]
Link: https://lore.kernel.org/rust-for-linux/DGE9DBH7X8CO.2EES6EX8UA5ZF@kernel.org/T/#mc17b9c0309ac10346b3d6c6bd8461488e7c73161 [2]

---
Changes since v3:
- Add `KnownSize` trait for documenting safety requirement of
  `ProjectIndex` and updated safety comments accordingly (Benno)
- Some comment rewording (Benno)
- Move code to be under `ptr` module.
- Link to v3: https://lore.kernel.org/rust-for-linux/20260302130223.134058-1-gary@kernel.org/

Changes since v2:
- Fix off-by-one issue (Aditya)
- Fix comment (Aditya)
- Link to v2: https://lore.kernel.org/rust-for-linux/20260226154656.3241736-1-gary@kernel.org/

Changes since v1:
- Squashed patch 2,3,4 so that all users are converted in single commit
  (Danilo)
- I discovered an additional soundness bug in dma_read/write macros
  where it can create misaligned access. This is addressed in this new
  version.
- Updated sample driver to have a function that does check instead use a
  budget-try block (Benno)
- Improved diagnostics when index projection is used on types that are
  not slices.
- Link to v1: https://lore.kernel.org/rust-for-linux/20260214053344.1994776-1-gary@garyguo.net/

---
Gary Guo (3):
  rust: ptr: add `KnownSize` trait to support DST size info extraction
  rust: ptr: add projection infrastructure
  rust: dma: use pointer projection infra for `dma_{read,write}` macro

 drivers/gpu/nova-core/gsp.rs      |  14 +-
 drivers/gpu/nova-core/gsp/boot.rs |   2 +-
 drivers/gpu/nova-core/gsp/cmdq.rs |  10 +-
 rust/kernel/dma.rs                | 114 +++++-------
 rust/kernel/lib.rs                |   4 +
 rust/kernel/ptr.rs                |  30 ++-
 rust/kernel/ptr/projection.rs     | 294 ++++++++++++++++++++++++++++++
 samples/rust/rust_dma.rs          |  30 +--
 scripts/Makefile.build            |   4 +-
 9 files changed, 411 insertions(+), 91 deletions(-)
 create mode 100644 rust/kernel/ptr/projection.rs


base-commit: 877552aa875839314afad7154b5a561889e87ea9
-- 
2.51.2