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Message-ID: <ZbP50nEIMqULfVuj@Boquns-Mac-mini.home>
Date: Fri, 26 Jan 2024 10:28:34 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...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>,
Kees Cook <keescook@...omium.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
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 3/3] rust: add abstraction for `struct page`
On Fri, Jan 26, 2024 at 01:33:46PM +0100, Alice Ryhl wrote:
> On Fri, Jan 26, 2024 at 1:47 AM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > On Wed, Jan 24, 2024 at 11:20:23AM +0000, Alice Ryhl wrote:
> > > + /// Maps the page and reads from it into the given buffer.
> > > + ///
> > > + /// # Safety
> > > + ///
> > > + /// Callers must ensure that `dest` is valid for writing `len` bytes.
> > > + pub unsafe fn read(&self, dest: *mut u8, offset: usize, len: usize) -> Result {
> > > + self.with_pointer_into_page(offset, len, move |from_ptr| {
> > > + // SAFETY: If `with_pointer_into_page` calls into this closure, then
> > > + // it has performed a bounds check and guarantees that `from_ptr` is
> > > + // valid for `len` bytes.
> > > + unsafe { ptr::copy(from_ptr, dest, len) };
> > > + Ok(())
> > > + })
> > > + }
> > > +
> > > + /// Maps the page and writes into it from the given buffer.
> > > + ///
> > > + /// # Safety
> > > + ///
> > > + /// Callers must ensure that `src` is valid for reading `len` bytes.
> > > + pub unsafe fn write(&self, src: *const u8, offset: usize, len: usize) -> Result {
> >
> > Use a slice like type as `src` maybe? Then the function can be safe:
> >
> > pub fn write<S: AsRef<[u8]>>(&self, src: S, offset: usize) -> Result
> >
> > Besides, since `Page` impl `Sync`, shouldn't this `write` and the
> > `fill_zero` be a `&mut self` function? Or make them both `unsafe`
> > because of potential race and add some safety requirement?
>
> Ideally, we don't want data races with these methods to be UB. They
I understand that, but in the current code, you can write:
CPU 0 CPU 1
===== =====
page.write(src1, 0, 8);
page.write(src2, 0, 8);
and it's a data race at kernel end. So my question is more how we can
prevent the UB ;-)
Regards,
Boqun
> could be mapped into the address space of a userspace process.
>
> Alice
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