[PATCH v14 0/8] Rust support for mm_struct, vm_area_struct, and mmap

[Alice Ryhl <aliceryhl@google.com>]

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.

MM folks, what do you prefer I do for the MAINTAINERS file? Would you
prefer that I add these files under MEMORY MANAGEMENT, or would you like
a separate entry similar to the BLOCK LAYER DEVICE DRIVER API [RUST]
entry? Or something else?

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Changes in v14:
- Rename VmArea* to Vma* as suggested by Liam.
- Update a few comments in patch 02.
- Link to v13: https://lore.kernel.org/r/20250203-vma-v13-0-2b998268a396@google.com

Changes in v13:
- Rebase on v6.14-rc1.
- Remove casts that are now unnecessary due to improved Rust/C integer
  type mappings.
- Link to v12: https://lore.kernel.org/r/20250115-vma-v12-0-375099ae017a@google.com

Changes in v12:
- Add additional documentation to modules at the top of mm.rs and virt.rs.
- Explain why the name Mm is used in commit message of patch 1.
- Expand zap_page_range_single with docs suggested by Lorenzo.
- Update safety comment in vm_insert_page
- Mention that VmAreaMixedMap is identical to VmAreaRef except for VM_MIXEDMAP.
- Update docs for as_mixedmap_vma.
- Add additional docs for VmAreaNew struct.
- Rename `get_read` -> `readable` and equivalent for write/exec.
- Use mut pointers for `from_raw` for VMAs.
- Update safety comment for fops_mmap.
- Add additional docs for MiscDevice::mmap.
- Don't introduce and immediately delete mmgrab_current.
- Reduce active_pid_ns comment at Andreas's suggestion and link to get_pid_ns.
- Fix documentation test in rust/kernel/task.rs.
- Fix warning about unused variables in lock_vma_under_rcu when
  CONFIG_PER_VMA_LOCK=n.
- Fix minor typos.
- Link to v11: https://lore.kernel.org/r/20241211-vma-v11-0-466640428fc3@google.com

Changes in v11:
- Add accessor for the vm_mm field of vm_area_struct.
- Pass the file to MiscDevice::mmap for consistency with
  https://lore.kernel.org/r/20241210-miscdevice-file-param-v3-1-b2a79b666dc5@google.com
- Link to v10: https://lore.kernel.org/r/20241129-vma-v10-0-4dfff05ba927@google.com

Changes in v10:
- Update docs for `set_io`.
- Check address in `zap_page_range_single`.
- Completely redo the last patch.
- Link to v9: https://lore.kernel.org/r/20241122-vma-v9-0-7127bfcdd54e@google.com

Changes in v9:
- Be more explicit about VmAreaNew being used with f_ops->mmap().
- Point out that clearing VM_MAYWRITE is irreversible.
- Use __vm_flags to set the flags.
- Use as_ and into_ prefixes for conversions.
- Update lock_vma_under_rcu docs and commit msg
- Mention that VmAreaRef::end is exclusive.
- Reword docs for zap_page_range_single.
- Minor fixes to flag docs.
- Add way to access current->mm without a refcount increment.
- Link to v8: https://lore.kernel.org/r/20241120-vma-v8-0-eb31425da66b@google.com

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@google.com

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@google.com

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@google.com

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@google.com

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@google.com

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@google.com

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@google.com

---
Alice Ryhl (8):
      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 VmaNew for f_ops->mmap()
      rust: miscdevice: add mmap support
      task: rust: rework how current is accessed

 rust/helpers/helpers.c    |   1 +
 rust/helpers/mm.c         |  50 +++++
 rust/kernel/lib.rs        |   1 +
 rust/kernel/miscdevice.rs |  44 +++++
 rust/kernel/mm.rs         | 341 +++++++++++++++++++++++++++++++++
 rust/kernel/mm/virt.rs    | 471 ++++++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/task.rs       | 247 ++++++++++++------------
 7 files changed, 1037 insertions(+), 118 deletions(-)
---
base-commit: a64dcfb451e254085a7daee5fe51bf22959d52d3
change-id: 20240723-vma-f80119f9fb35

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