linux-kernel - Re: [PATCH v3] rust: mm: add abstractions for mm_struct and vm_area

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Message-ID: <ZquVcyeLqGGRbgx-@pollux>
Date: Thu, 1 Aug 2024 16:02:27 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Matthew Wilcox <willy@...radead.org>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v3] rust: mm: add abstractions for mm_struct and
 vm_area_struct

On Thu, Aug 01, 2024 at 12:58:45PM +0000, Alice Ryhl wrote:
> This is a follow-up to the page abstractions [1] that were recently
> merged in 6.11. Rust Binder will need these abstractions to manipulate
> the vma in its implementation of the mmap fop on the Binder file.
> 
> This patch is based on Wedson's implementation on the old rust branch,
> but has been changed significantly. All mistakes are Alice's.
> 
> Link: https://lore.kernel.org/r/20240528-alice-mm-v7-4-78222c31b8f4@google.com [1]
> Co-developed-by: Wedson Almeida Filho <wedsonaf@...il.com>
> Signed-off-by: Wedson Almeida Filho <wedsonaf@...il.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.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
> ---
>  rust/helpers.c         |  61 +++++++++
>  rust/kernel/lib.rs     |   1 +
>  rust/kernel/mm.rs      | 337 +++++++++++++++++++++++++++++++++++++++++++++++++
>  rust/kernel/mm/virt.rs | 204 ++++++++++++++++++++++++++++++
>  rust/kernel/types.rs   |   9 ++
>  5 files changed, 612 insertions(+)
> 
> diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs
> new file mode 100644
> index 000000000000..ed2db893fb79
> --- /dev/null
> +++ b/rust/kernel/mm.rs
> @@ -0,0 +1,337 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +// Copyright (C) 2024 Google LLC.
> +
> +//! Memory management.
> +//!
> +//! C header: [`include/linux/mm.h`](../../../../include/linux/mm.h)

NIT: srctree

> +
> +    /// Returns a raw pointer to the inner `mm_struct`.
> +    #[inline]
> +    pub fn as_raw(&self) -> *mut bindings::mm_struct {
> +        self.mm.get()
> +    }
> +
> +    /// Obtain a reference from a raw pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// The caller must ensure that `ptr` points at an `mm_struct`, and that it is not deallocated
> +    /// during the lifetime 'a.
> +    #[inline]
> +    pub unsafe fn from_raw_mm<'a>(ptr: *const bindings::mm_struct) -> &'a Mm {

I'd just call this `from_raw`, like you call the counterpart `as_raw` above.
Same goes for `MmWithUser` and `VmArea`.

> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index bd189d646adb..143a2bf06941 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -366,6 +366,15 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
>              _p: PhantomData,
>          }
>      }
> +
> +    /// Pass ownership of the refcount to a raw pointer.
> +    pub fn into_raw(self) -> NonNull<T> {
> +        let ptr = self.ptr;
> +        // Skip the destructor.
> +        core::mem::forget(self);
> +
> +        ptr
> +    }

I think this should be a separate patch.

>  }
>  
>  impl<T: AlwaysRefCounted> Clone for ARef<T> {
> 
> ---
> base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b
> change-id: 20240723-vma-f80119f9fb35
> 
> Best regards,
> -- 
> Alice Ryhl <aliceryhl@...gle.com>
> 
>