This updates the vm_area_struct support to use the approach we discussed
at LPC where there are several different Rust wrappers for
vm_area_struct depending on the kind of access you have to the vma. Each
case allows a different set of operations on the vma.

This series depends on vfs.rust.file and char-misc-next which are
scheduled to land upstream in the current merge window.

---
Changes in v8:
- Split series into more commits to ease review.
- Improve read locks based on Lorenzo's doc: either the mmap or vma lock
  can be used.
- Get rid of mmap write lock because it's possible to avoid the need for
  it.
- Do not allow invalid flag combinations on VmAreaNew.
- Link to v7: https://lore.kernel.org/r/20241014-vma-v7-0-01e32f861195@...

Changes in v7:
- Make the mmap read/write lock guards respect strict owner semantics.
- Link to v6: https://lore.kernel.org/r/20241010-vma-v6-0-d89039b6f573@...

Changes in v6:
- Introduce VmArea{Ref,Mut,New} distinction.
- Add a second patchset for miscdevice.
- Rebase on char-misc-next (currently on v6.12-rc2).
- Link to v5: https://lore.kernel.org/r/20240806-vma-v5-1-04018f05de2b@...

Changes in v5:
- Rename VmArea::from_raw_vma to from_raw.
- Use Pin for mutable VmArea references.
- Go through `ARef::from` in `mmgrab_current`.
- Link to v4: https://lore.kernel.org/r/20240802-vma-v4-1-091a87058a43@...

Changes in v4:
- Pull out ARef::into_raw into a separate patch.
- Update invariants and struct documentation.
- Rename from_raw_mm to from_raw.
- Link to v3: https://lore.kernel.org/r/20240801-vma-v3-1-db6c1c0afda9@...

Changes in v3:
- Reorder entries in mm.rs.
- Use ARef for mmput_async helper.
- Clarify that VmArea requires you to hold the mmap read or write lock.
- Link to v2: https://lore.kernel.org/r/20240727-vma-v2-1-ab3e5927dc3a@...

Changes in v2:
- mm.rs is redesigned from scratch making use of AsRef
- Add notes about whether destructors may sleep
- Rename Area to VmArea
- Link to v1: https://lore.kernel.org/r/20240723-vma-v1-1-32ad5a0118ee@...

---
Alice Ryhl (7):
      mm: rust: add abstraction for struct mm_struct
      mm: rust: add vm_area_struct methods that require read access
      mm: rust: add vm_insert_page
      mm: rust: add lock_vma_under_rcu
      mm: rust: add mmput_async support
      mm: rust: add VmAreaNew
      rust: miscdevice: add mmap support

 rust/helpers/helpers.c    |   1 +
 rust/helpers/mm.c         |  50 ++++++
 rust/kernel/lib.rs        |   1 +
 rust/kernel/miscdevice.rs |  28 ++++
 rust/kernel/mm.rs         | 345 +++++++++++++++++++++++++++++++++++++++
 rust/kernel/mm/virt.rs    | 404 ++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 829 insertions(+)
---
base-commit: 7f219f5002eb0ce2b12562127aeb0521bbf2146e
change-id: 20240723-vma-f80119f9fb35

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>