Re: [PATCH v7 0/2] Rust support for mm_struct, vm_area_struct, and mmap for miscdevice

Boqun Feng
2024-10-30T19:54:52Z

Hi Lorenzo,

On Wed, Oct 30, 2024 at 06:52:34PM +0000, Lorenzo Stoakes wrote:
> On Mon, Oct 14, 2024 at 09:29:50AM +0000, Alice Ryhl wrote:
> > The first patch introduces mm_struct and vm_area_struct abstractions,
> > and the second patch uses them for miscdevice.
> >
> > This updates the vm_area_struct support to use the approach we discussed
> > at LPC where there are three different types depending on the kind of
> > access you have to the vma. You either have read access, write access,
> > or you are initializing it. Each case allows a larger set of operations
> > on the vma.
> >
> > The first patch in this series depends on vfs.rust.file for
> > NotThreadSafe. The second patch in this series depends on char-misc-next
> > for the base miscdevice implementation.
> >
>
> Hi Alice,
>
> Just to be clear - I am very keen in seeing this land, and will take a look
> a this from a VMA and locking perspective.
>

Thanks!

> I've been tied up with other work which has delayed me, but am
> simultaneously working on documenting VMA locking (with various tricky ins
> and outs around 'implicit' rules) which directly feeds into ensuring the
> rust abstraction correctly matches expectation on the locking side of
> things.
>
> So I'd ideally like to get this doc update done first before reviewing, to
> ensure we have good clarity on locking, but I think perhaps a good way is
> for me to try to do both in conjunction with one another (will cc- you on
> docs series when I send it!)
>

Please Cc me as well, thanks!

Regards,
Boqun

> In any case - I will absolutely give this my attention as soon as I am able
> to.
>
> Relatedly - we've encountered issues recently in relation to locking
> subtleties so this is _highly_ pertinent and equally _highly_ motivating
> for having compiler help on this + a programmatic representation in rust.
>
> I know Willy is in full support of this effort too, we are all keen to see
> things move forward.
>
> Thank you for doing this! :)
>
> Best, Lorenzo
>
> > ---
> > 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 (2):
> > rust: mm: add abstractions for mm_struct and vm_area_struct
> > rust: miscdevice: add mmap support
> >
> > rust/helpers/helpers.c | 1 +
> > rust/helpers/mm.c | 55 +++++++
> > rust/kernel/lib.rs | 1 +
> > rust/kernel/miscdevice.rs | 24 ++++
> > rust/kernel/mm.rs | 357 ++++++++++++++++++++++++++++++++++++++++++++++
> > rust/kernel/mm/virt.rs | 264 ++++++++++++++++++++++++++++++++++
> > 6 files changed, 702 insertions(+)
> > ---
> > base-commit: 2d424646119f28780f3963811025c05ea848b85f
> > change-id: 20240723-vma-f80119f9fb35
> >
> > Best regards,
> > --
> > Alice Ryhl <aliceryhl@google.com>
> >