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Date: Tue, 14 May 2024 10:27:57 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Alice Ryhl <aliceryhl@google.com>
Cc: Miguel Ojeda <ojeda@kernel.org>, Matthew Wilcox <willy@infradead.org>,
 Al Viro <viro@zeniv.linux.org.uk>, Kees Cook <keescook@chromium.org>, Alex
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 <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 2/4] uaccess: always export _copy_[from|to]_user with
 CONFIG_RUST
Message-Id: <20240514102757.b7034966a58e6cf44d75dc7d@linux-foundation.org>
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References: <20240418-alice-mm-v6-0-cb8f3e5d688f@google.com>
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On Thu, 18 Apr 2024 08:59:18 +0000 Alice Ryhl <aliceryhl@google.com> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
> 
> Rust code needs to be able to access _copy_from_user and _copy_to_user
> so that it can skip the check_copy_size check in cases where the length
> is known at compile-time, mirroring the logic for when C code will skip
> check_copy_size. To do this, we ensure that exported versions of these
> methods are available when CONFIG_RUST is enabled.
> 
> Alice has verified that this patch passes the CONFIG_TEST_USER_COPY test
> on x86 using the Android cuttlefish emulator.
> 
>  ...
>
> -#ifdef INLINE_COPY_TO_USER
>  static inline __must_check unsigned long
> -_copy_to_user(void __user *to, const void *from, unsigned long n)
> +_inline_copy_to_user(void __user *to, const void *from, unsigned long n)
>  {

I think it would be helpful to have some comments in here describing
why we're doing this _inline_* thing.  What problem is it avoiding?