linux-kernel - Re: [PATCH 3/5] mm: export zap_page_range_single and list_lru

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Message-ID: <39931d87-7e50-4e67-9f9a-3980f39de16c@lucifer.local>
Date: Thu, 5 Feb 2026 12:28:23 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: "David Hildenbrand (arm)" <david@...nel.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <lossin@...nel.org>,
        Andreas Hindborg <a.hindborg@...nel.org>,
        Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
        kernel-team@...roid.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-mm@...ck.org, rust-for-linux@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 3/5] mm: export zap_page_range_single and list_lru_add/del

On Thu, Feb 05, 2026 at 01:24:09PM +0100, Miguel Ojeda wrote:
> On Thu, Feb 5, 2026 at 12:58 PM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > What??
> >
> > Alice - can you confirm rust isn't exporting stuff that isn't explicitly marked
> > EXPORT_SYMBOL*() for use by other rust modules?
> >
> > It's important we keep this in sync, otherwise rust is overriding kernel policy.
>
> Currently, Rust GPL-exports every mangled symbol from the `kernel`
> crate. To call something you would need to be a Rust caller (not C --
> that is not supported at all, even if technically you could hack
> something up) and the Rust API would then need to give you access to
> it (i.e. you need to be able to pass the Rust language rules, e.g.
> being public etc.).
>
> In this case if we are talking about the `VmaRef` type, someone that
> can get a reference to a value of that type could then call the
> `zap_page_range_single` method. That in turns would try to call the C
> one, but that one is not exported, right? So it should be fine.
>

OK cool. Thanks for the explanation.

> In the future, for Rust, we may specify whether a particular crate
> exports or not (and perhaps even allow to export non-GPL, but
> originally it was decided to only export GPL stuff to be on the safe
> side; and perhaps in certain namespaces etc.).

We'd definitely need to keep this in sync with C exports, maybe we can find
a nice way of doing/checking this.

Generally we're _very_ conservative about exports, and actually it'd be
nice if maybe rust only provided GPL ones. The GPL is a good thing :) But I
guess we can figure that out later.

>
> Cheers,
> Miguel

Cheers, Lorenzo