linux-kernel - Re: [PATCH V9 15/17] rust: cpufreq: Extend abstractions for driver registration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Z_kD5G3WhcYlgqmr@cassiopeiae>
Date: Fri, 11 Apr 2025 13:58:28 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Danilo Krummrich <dakr@...hat.com>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...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@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	linux-pm@...r.kernel.org,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
	rust-for-linux@...r.kernel.org,
	Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
	Erik Schilling <erik.schilling@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Joakim Bech <joakim.bech@...aro.org>, Rob Herring <robh@...nel.org>,
	Yury Norov <yury.norov@...il.com>, Burak Emir <bqe@...gle.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Russell King <linux@...linux.org.uk>, linux-clk@...r.kernel.org,
	Michael Turquette <mturquette@...libre.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 15/17] rust: cpufreq: Extend abstractions for driver
 registration

On Fri, Apr 11, 2025 at 04:25:14PM +0530, Viresh Kumar wrote:
> +pub struct Registration<T: Driver> {
> +    drv: KBox<UnsafeCell<bindings::cpufreq_driver>>,
> +    _p: PhantomData<T>,
> +}
> +
> +// SAFETY: `Registration` doesn't offer any methods or access to fields when shared between threads
> +// or CPUs, so it is safe to share it.
> +unsafe impl<T: Driver> Sync for Registration<T> {}
> +
> +#[allow(clippy::non_send_fields_in_send_ty)]
> +// SAFETY: Registration with and unregistration from the cpufreq subsystem can happen from any
> +// thread.  Additionally, `T::Data` (which is dropped during unregistration) is `Send`, so it is
> +// okay to move `Registration` to different threads.
> +unsafe impl<T: Driver> Send for Registration<T> {}
> +
> +impl<T: Driver> Registration<T> {
> +    /// Registers a CPU frequency driver with the cpufreq core.
> +    pub fn new(name: &'static CStr, data: T::Data, flags: u16, boost: bool) -> Result<Self> {

Do you really need the private data? It seems to be used by only very few
drivers in C either.

If yes, I think you have to split this up into a CpufreqDriver structure and a
separate Registration. Otherwise you won't ever get access to the private data
again, after Registration::new_foreign_owned().

Note that we typically want Registration::new_foreign_owned(), because it
implies the guaranteed "fence" for where we can safely consider a device to be
bound. If we'd give out a Registration instance instead, the driver can
arbitrarily extend its lifetime across the remove() boundary.

If no, it seems to me that you can even avoid allocating a struct cpufreq_driver
dynamically and make it const instead. The fields name, boost_enabled and flags
could be required consts in your cpufreq::Driver trait.