Re: [PATCH v2 1/2] rust_binder: check ownership before using vma

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Aug 24, 2026 at 10:48:08PM +0300, Artem Lytkin wrote:
> On Wed, Feb 18, 2026, Alice Ryhl wrote:
> > The plan is to introduce more vma
> > abstractions to avoid this unsafe access to vm_ops and vm_private_data,
> > but for now let's start with the simplest possible fix.
> [...]
> > (We probably still want to do both, but
> > the vm_ops->close callback will be added later as part of the follow-up
> > vma API changes.)
> 
> Alice, is that follow-up still on your list, or would you rather someone
> else took it?
> 
> I'd like to add the missing pieces to kernel::mm::virt: a VmOperations
> trait with open, close and fault, a typed way to install it together
> with the private data on a VmaNew, a VmFault wrapper, and a PFN-map
> typestate next to VmaMixedMap with vmf_insert_pfn_prot() on it. Binder
> would then drop BINDER_VM_OPS and the raw vm_ops pointer compare and get
> a close callback like the C driver has. Tyr needs the fault and PFN-map
> half of that for its user MMIO mmap. The first two patches of
> Collabora's Tyr series are the pgprot_noncached and pgoff helpers; they
> have had no replies since 7 May, so I'd build on those rather than
> duplicate them:
> 
>   https://lore.kernel.org/all/20260507-tyr-mmap-v1-0-eec048a23c25@collabora.com/

I have a draft for the vm_open callback somewhere and it's still on my
todo-list, but I'm not actively working on it right now. I'd be happy to
let someone else work on it, but it's somewhat nontrivial, so perhaps we
should have a call to discuss the design to work out the details?

> One design question first, for you and Lorenzo. f_op->mmap is
> deprecated in favour of mmap_prepare, where a driver sets desc->vm_ops
> instead of touching the vma, and the Rust side only has the old mmap
> path today. Should the vm_ops abstraction be built around mmap_prepare
> from the start, with a Rust mmap_prepare hook for miscdevice next to
> it, or is landing it on the existing VmaNew an acceptable first step?

Lorenzo, where can I learn more about this new mmap_prepare API? What
are the main differences?

Alice