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 2490D1D8DFB for ; Sat, 17 Jan 2026 11:19:28 +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=1768648769; cv=none; b=d9OExHUaygZq5i1Gydx2cG5VKe7RVOZ8YzKI63SfdNK54TIGkjR7g6T55+QeW4uWnVLwZ9sfOT+KOiw1Qp0nHKZPnx6KKN+DRu0UxBDthIPvgHTvDcwcYCdzWV9tQhhJpx3e/avR4X6Zfy5JHfAnmwi9GLQ40ANMumLEsrEBLOg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768648769; c=relaxed/simple; bh=fB7T6W9WSy/Dus3CVGYgcLzz7Jj4LHH2sIpcmY23ob0=; h=Mime-Version:Content-Type:Date:Message-Id:Cc:To:From:Subject: References:In-Reply-To; b=WE1sIauQgWX+EUXHOpCG7YkBOvFvJdXIwJVTzn0a55MIIOsyl0VpccQL0xDCR6esJvxlrjDrHoHQamOQ4764VbLDKlJfyezqcJ6fcOFoPYG4KGbrje4YEB+5PZaw5gTO+jHDxODpbewQwq6w1KD6nXFBQXksVJYIpLYPQVgSoMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BYuMSjXE; 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="BYuMSjXE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14A62C4CEF7; Sat, 17 Jan 2026 11:19:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768648768; bh=fB7T6W9WSy/Dus3CVGYgcLzz7Jj4LHH2sIpcmY23ob0=; h=Date:Cc:To:From:Subject:References:In-Reply-To:From; b=BYuMSjXEXi8nUfo/eWyB6QoP1ih+mWBxgI24P8d04YVEgPr8mBpcPuPJgvNuWSlqd SsHdniX+Mtx2TxypWIgjd/JZoe3u0RNuJNlyzXqcn+1G6UD80mHKa/m908BJozDmZT bC4bNWWuyZfgOYci7wYME7LiiFAJMOl66ITP6nBkMOz8zLMCoNLanp06vhoh0eT2g4 OFhzO/XSQCMpCxokpYpHeeMtIfMRCZkoSruzpwUbtVMDCSM7EwiqFndb5vSoflLrnZ 13Brw5I2FLjRDfURQPMae49HPt+/1tI3UPPXnEdo5LHb57xBJdQX04BgkTwe9XVRam jbWRCkPYjChWg== Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sat, 17 Jan 2026 12:19:25 +0100 Message-Id: Cc: "Matthew Maurer" , "Gary Guo" , "John Hubbard" , "Joel Fernandes" , "Alexandre Courbot" , "Alice Ryhl" , , To: "Timur Tabi" From: "Danilo Krummrich" Subject: Re: [PATCH v5 3/8] rust: uaccess: add UserSliceWriter::write_buffer() for raw pointer writes References: <20260116214959.641032-1-ttabi@nvidia.com> <20260116214959.641032-4-ttabi@nvidia.com> In-Reply-To: (Really Cc: Alice :) On Sat Jan 17, 2026 at 12:18 PM CET, Danilo Krummrich wrote: > (Cc: Alice) > > Alice, for context, this is used when exporting a DMA buffer through debu= gfs, > while the DMA buffer may be in use by the device, i.e. no slice can be cr= eated. > > On Fri Jan 16, 2026 at 10:49 PM CET, Timur Tabi wrote: >> Add a new method to UserSliceWriter that copies data from a raw kernel >> pointer to userspace, without requiring a Rust slice reference. >> >> The method takes: >> - data: raw pointer to the source buffer >> - len: total size of the source buffer (for bounds checking) >> - offset: byte offset into the source buffer to start copying from >> - count: number of bytes to copy >> >> The method is marked unsafe because the caller must ensure the pointer >> is valid for the specified length and that the memory is not mutated >> during the call. >> >> Signed-off-by: Timur Tabi >> --- >> rust/kernel/uaccess.rs | 50 ++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 50 insertions(+) >> >> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs >> index f989539a31b4..8bbb0084abb1 100644 >> --- a/rust/kernel/uaccess.rs >> +++ b/rust/kernel/uaccess.rs >> @@ -481,6 +481,56 @@ pub fn write_slice(&mut self, data: &[u8]) -> Resul= t { >> Ok(()) >> } >> =20 >> + /// Writes raw data to this user pointer from a raw kernel pointer. >> + /// >> + /// This is similar to [`Self::write_slice`] but takes a raw pointe= r instead of a slice, >> + /// along with a total buffer length, an offset into the that buffe= r, and a count of bytes >> + /// to copy. >> + /// >> + /// Returns error if the offset+count exceeds the buffer size. >> + /// >> + /// Fails with [`EFAULT`] if the write happens on a bad address, or= if the write goes out of >> + /// bounds of this [`UserSliceWriter`]. This call may modify the as= sociated userspace slice >> + /// even if it returns an error. >> + /// >> + /// # Safety >> + /// >> + /// - `data` must point to a valid memory region of at least `len` = bytes that remains allocated >> + /// for the duration of this call. >> + /// >> + /// Note: Unlike [`Self::write_slice`], this method does not requir= e exclusive access to the >> + /// source memory. The memory may be concurrently modified by other= threads or hardware (e.g., >> + /// DMA buffers). In such cases, the copied data may be inconsisten= t, but this does not cause >> + /// undefined behavior. >> + pub unsafe fn write_buffer( >> + &mut self, >> + data: *const u8, >> + len: usize, >> + offset: usize, >> + count: usize, >> + ) -> Result { > > Instead of this we could probably also add a safe method write_dma() that= takes > a dma::CoherentAllocation instead. Once we have generic I/O in place,= this > could be replaced with a generic write_io() method.