From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A59D515B119; Wed, 23 Oct 2024 08:42:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729672952; cv=none; b=sFM6nE/AmKg2M9fD0mnKNnHqO/2dCy5S3L3nWEV3bMQmfSa5DJVkJqv7hwt1l8OkF/ivNlZZqWpihOOwiNB4ePq1D9vkIalW566U0sZyJFmzc8Jauxt8aAY1SJDhf1BhmzkPCbpVuNtqn0rgR5U+p3tUVHpvAFDEh1jOotkFb+8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729672952; c=relaxed/simple; bh=MUvsm0SJiAa7QJxtfIg1c1B+VPR/9fnWUOukgzeCebI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=doj6SA3bjTnTFpVpJNz9OHYScZAO7k5xsFzMfdxCE2qWi6B3VLGmdKAuxQ+0dtVKvEit0x0cvF8K9/2s8dHZFGaK5W+hweGcRd3rremN0ZJlsOOLTQavJw4NXLhvKHC5f8xxGRVR35Gl3KrvwFMkqoevcg8+gi8/X4MyICo+J4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=log0oo+M; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="log0oo+M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B931C4CEC6; Wed, 23 Oct 2024 08:42:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729672952; bh=MUvsm0SJiAa7QJxtfIg1c1B+VPR/9fnWUOukgzeCebI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=log0oo+MY70lsYlmUABQukyclUAvCVf9UoVj1hhSijAYjdobWreM4J9NUjpM/jw6z E+UXAn6DuLEgloK0G0xE/ez0OBaQ6FsMidPIlW5JXN0RQsvoNNgxR/ZuEGQb31MRL5 gQu0QQP1QiGU18fU4QDHaP2RxZxEZE6m72E64jKragb3CEKOJ+N/QYfWb8DnCd7s/6 6/jgkqaTsdY72cHSt7iIY/qWr+9HrwDmb9QlLV/VbprAkmJRI/IDKVxrd6MHt3990T xgooWawOO01Q7OJfzaGdAcFv3zJPNKpjcTuG7IQueDVXCVDEGjUmcwLYBD45LSeKg/ kxON/qpD4Pa5A== Date: Wed, 23 Oct 2024 10:42:27 +0200 From: Danilo Krummrich To: Abdiel Janulgue Cc: rust-for-linux@vger.kernel.org, aliceryhl@google.com, dakr@redhat.com, linux-kernel@vger.kernel.org, airlied@redhat.com, miguel.ojeda.sandonis@gmail.com, boqun.feng@gmail.com Subject: Re: [PATCH v2 3/5] rust: page: Extend support to vmalloc_to_page Message-ID: References: <20241022224832.1505432-1-abdiel.janulgue@gmail.com> <20241022224832.1505432-4-abdiel.janulgue@gmail.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241022224832.1505432-4-abdiel.janulgue@gmail.com> On Wed, Oct 23, 2024 at 01:44:47AM +0300, Abdiel Janulgue wrote: > Extend Page to support pages that are not allocated by the constructor, for > example, those returned by vmalloc_to_page(). Since we don't own those pages > we shouldn't Drop them either. Hence we take advantage of the switch to Opaque > so we can cast to a Page pointer from a struct page pointer and be able to > retrieve the reference on an existing struct page mapping. In this case > no destructor will be called since we are not instantiating a new Page instance. > > Signed-off-by: Abdiel Janulgue > --- > rust/kernel/page.rs | 32 ++++++++++++++++++++++++++++++-- > 1 file changed, 30 insertions(+), 2 deletions(-) > > diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs > index a8288c15b860..465928986f4b 100644 > --- a/rust/kernel/page.rs > +++ b/rust/kernel/page.rs > @@ -31,11 +31,12 @@ pub const fn page_align(addr: usize) -> usize { > (addr + (PAGE_SIZE - 1)) & PAGE_MASK > } > > -/// A pointer to a page that owns the page allocation. > +/// A pointer to a page that may own the page allocation. > /// > /// # Invariants > /// > -/// The pointer is valid, and has ownership over the page. > +/// The pointer is valid, and has ownership over the page if the page is allocated by this > +/// abstraction. > #[repr(transparent)] > pub struct Page { > page: Opaque, > @@ -88,6 +89,33 @@ pub fn alloc_page(flags: Flags) -> Result, AllocError> { > Ok(unsafe { Owned::to_owned(ptr) }) > } > > + /// This is just a wrapper to vmalloc_to_page which returns an existing page mapping, hence In documentation, try to avoid filler words, such as "just". Better say something like: "This is an abstraction around the C `vmalloc_to_page()` function. Note that by a call to this function the caller doesn't take ownership of the returned `Page` [...]." > + /// we don't take ownership of the page. Returns an error if the pointer is null or if it > + /// is not returned by vmalloc(). > + pub fn vmalloc_to_page<'a>( > + cpu_addr: *const core::ffi::c_void When you have a raw pointer argument in your function it becomes unsafe by definition. I also think it would also be better to pass a `NonNull` instead. > + ) -> Result<&'a Self, AllocError> Please don't use `AllocError`. We're not allocating anything here. Anyway, do we need this as a separate function at all? > + { > + if cpu_addr.is_null() { > + return Err(AllocError); > + } > + // SAFETY: We've checked that the pointer is not null, so it is safe to call this method. > + if unsafe { !bindings::is_vmalloc_addr(cpu_addr) } { > + return Err(AllocError); > + } > + // SAFETY: We've initially ensured the pointer argument to this function is not null and > + // checked for the requirement the the buffer passed to it should be allocated by vmalloc, > + // so it is safe to call this method. > + let page = unsafe { bindings::vmalloc_to_page(cpu_addr) }; > + if page.is_null() { > + return Err(AllocError); > + } I think those should all return `EINVAL` instead. > + // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::page`. > + // SAFETY: We just successfully allocated a page, therefore dereferencing > + // the page pointer is valid. > + Ok(unsafe { &*page.cast() }) > + } > + > /// Returns a raw pointer to the page. > pub fn as_ptr(&self) -> *mut bindings::page { > self.page.get() > -- > 2.43.0 >