linux-kernel - Re: [PATCH v5 4/4] rust: add abstraction for `struct page`

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Message-ID: <87il0jm4fr.fsf@metaspace.dk>
Date: Mon, 15 Apr 2024 10:10:48 +0200
From: Andreas Hindborg <nmi@...aspace.dk>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,  Matthew Wilcox <willy@...radead.org>,
  Al Viro <viro@...iv.linux.org.uk>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Kees Cook <keescook@...omium.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>,  Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>,  Arve Hjønnevåg
 <arve@...roid.com>,  Todd
 Kjos <tkjos@...roid.com>,  Martijn Coenen <maco@...roid.com>,  Joel
 Fernandes <joel@...lfernandes.org>,  Carlos Llamas <cmllamas@...gle.com>,
  Suren Baghdasaryan <surenb@...gle.com>,  Arnd Bergmann <arnd@...db.de>,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org,
  rust-for-linux@...r.kernel.org,  Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH v5 4/4] rust: add abstraction for `struct page`

Alice Ryhl <aliceryhl@...gle.com> writes:

> Adds a new struct called `Page` that wraps a pointer to `struct page`.
> This struct is assumed to hold ownership over the page, so that Rust
> code can allocate and manage pages directly.
>
> The page type has various methods for reading and writing into the page.
> These methods will temporarily map the page to allow the operation. All
> of these methods use a helper that takes an offset and length, performs
> bounds checks, and returns a pointer to the given offset in the page.
>
> This patch only adds support for pages of order zero, as that is all
> Rust Binder needs. However, it is written to make it easy to add support
> for higher-order pages in the future. To do that, you would add a const
> generic parameter to `Page` that specifies the order. Most of the
> methods do not need to be adjusted, as the logic for dealing with
> mapping multiple pages at once can be isolated to just the
> `with_pointer_into_page` method.
>
> Rust Binder needs to manage pages directly as that is how transactions
> are delivered: Each process has an mmap'd region for incoming
> transactions. When an incoming transaction arrives, the Binder driver
> will choose a region in the mmap, allocate and map the relevant pages
> manually, and copy the incoming transaction directly into the page. This
> architecture allows the driver to copy transactions directly from the
> address space of one process to another, without an intermediate copy
> to a kernel buffer.
>
> This code is based on Wedson's page abstractions from the old rust
> branch, but it has been modified by Alice by removing the incomplete
> support for higher-order pages, by introducing the `with_*` helpers
> to consolidate the bounds checking logic into a single place, and by
> introducing gfp flags.
>
> 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>
> ---

Reviewed-by: Andreas Hindborg <a.hindborg@...sung.com>