From: Benno Lossin <benno.lossin@proton.me>
To: Boqun Feng <boqun.feng@gmail.com>, Alice Ryhl <aliceryhl@google.com>
Cc: "Miguel Ojeda" <ojeda@kernel.org>,
"Matthew Wilcox" <willy@infradead.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kees Cook" <keescook@chromium.org>,
"Alex Gaynor" <alex.gaynor@gmail.com>,
"Wedson Almeida Filho" <wedsonaf@gmail.com>,
"Gary Guo" <gary@garyguo.net>,
"Björn Roy Baron" <bjorn3_gh@protonmail.com>,
"Andreas Hindborg" <a.hindborg@samsung.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Arve Hjønnevåg" <arve@android.com>,
"Todd Kjos" <tkjos@android.com>,
"Martijn Coenen" <maco@android.com>,
"Joel Fernandes" <joel@joelfernandes.org>,
"Carlos Llamas" <cmllamas@google.com>,
"Suren Baghdasaryan" <surenb@google.com>,
"Arnd Bergmann" <arnd@arndb.de>,
"Trevor Gross" <tmgross@umich.edu>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
rust-for-linux@vger.kernel.org,
"Christian Brauner" <brauner@kernel.org>
Subject: Re: [PATCH v6 4/4] rust: add abstraction for `struct page`
Date: Thu, 18 Apr 2024 22:08:40 +0000 [thread overview]
Message-ID: <87dc4cdf-ccf6-4b08-8915-313aad313f93@proton.me> (raw)
In-Reply-To: <ZiFsCLb-BZWbBHsu@boqun-archlinux>
On 18.04.24 20:52, Boqun Feng wrote:
> On Thu, Apr 18, 2024 at 08:59:20AM +0000, Alice Ryhl wrote:
>> + /// Runs a piece of code with a raw pointer to a slice of this page, with bounds checking.
>> + ///
>> + /// If `f` is called, then it will be called with a pointer that points at `off` bytes into the
>> + /// page, and the pointer will be valid for at least `len` bytes. The pointer is only valid on
>> + /// this task, as this method uses a local mapping.
>> + ///
>> + /// If `off` and `len` refers to a region outside of this page, then this method returns
>> + /// `EINVAL` and does not call `f`.
>> + ///
>> + /// # Using the raw pointer
>> + ///
>> + /// It is up to the caller to use the provided raw pointer correctly. The pointer is valid for
>> + /// `len` bytes and for the duration in which the closure is called. The pointer might only be
>> + /// mapped on the current thread, and when that is the case, dereferencing it on other threads
>> + /// is UB. Other than that, the usual rules for dereferencing a raw pointer apply: don't cause
>> + /// data races, the memory may be uninitialized, and so on.
>> + ///
>> + /// If multiple threads map the same page at the same time, then they may reference with
>> + /// different addresses. However, even if the addresses are different, the underlying memory is
>> + /// still the same for these purposes (e.g., it's still a data race if they both write to the
>> + /// same underlying byte at the same time).
>> + fn with_pointer_into_page<T>(
>> + &self,
>> + off: usize,
>> + len: usize,
>> + f: impl FnOnce(*mut u8) -> Result<T>,
>
> I wonder whether the way to go here is making this function signature:
>
> fn with_slice_in_page<T> (
> &self,
> off: usize,
> len: usize,
> f: iml FnOnce(&UnsafeCell<[u8]>) -> Result<T>
> ) -> Result<T>
>
> , because in this way, it makes a bit more clear that what memory that
> `f` can access, in other words, the users are less likely to use the
> pointer in a wrong way.
>
> But that depends on whether `&UnsafeCell<[u8]>` is the correct
> abstraction and the ecosystem around it: for example, I feel like these
> two functions:
>
> fn len(slice: &UnsafeCell<[u8]>) -> usize
> fn as_ptr(slice: &UnsafeCell<[u8]>) -> *mut u8
>
> should be trivially safe, but I might be wrong. Again this is just for
> future discussion.
I think the "better" type would be `&[UnsafeCell<u8>]`. Since there you
can always access the length.
Another question would be if page allows for uninitialized bits, in that
case, we would need `&[Opaque<u8>]`.
But I don't remember how to get a valid raw pointer from
`&[UnsafeCell<u8>]`.
--
Cheers,
Benno
next prev parent reply other threads:[~2024-04-18 22:08 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-18 8:59 [PATCH v6 0/4] Memory management patches needed by Rust Binder Alice Ryhl
2024-04-18 8:59 ` [PATCH v6 1/4] rust: uaccess: add userspace pointers Alice Ryhl
2024-04-19 17:11 ` Boqun Feng
2024-04-19 18:12 ` Alice Ryhl
2024-04-18 8:59 ` [PATCH v6 2/4] uaccess: always export _copy_[from|to]_user with CONFIG_RUST Alice Ryhl
2024-04-18 8:59 ` [PATCH v6 3/4] rust: uaccess: add typed accessors for userspace pointers Alice Ryhl
2024-04-18 13:01 ` Benno Lossin
2024-04-18 13:17 ` Alice Ryhl
2024-04-18 16:23 ` Benno Lossin
2024-04-18 17:19 ` Boqun Feng
2024-04-18 19:35 ` Alice Ryhl
2024-04-18 20:01 ` Boqun Feng
2024-04-18 17:52 ` Trevor Gross
2024-04-25 16:13 ` Gary Guo
2024-04-26 7:13 ` Alice Ryhl
2024-04-18 8:59 ` [PATCH v6 4/4] rust: add abstraction for `struct page` Alice Ryhl
2024-04-18 18:52 ` Boqun Feng
2024-04-18 22:08 ` Benno Lossin [this message]
2024-04-18 22:56 ` Boqun Feng
2024-04-18 23:04 ` Boqun Feng
2024-04-19 8:36 ` Benno Lossin
2024-04-19 17:23 ` Boqun Feng
2024-04-19 19:24 ` Benno Lossin
2024-04-19 19:35 ` Boqun Feng
2024-04-25 16:20 ` Gary Guo
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