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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768648696; bh=r8pFE19enbEpY7dhMp0/C2AB6nWk5mDSkT6a80RWyqI=; h=Date:To:From:Subject:Cc:References:In-Reply-To:From; b=p4W5icmmAKGZxgj0llhic9EJcPcciAHWRUgg2ptPSvqsDsCEdphtvZcB2aL0CD4V1 hlXryIpiW8W3O77m/jBm+bG57x7ds0iv3npPjWknrv/l9a9xIvr1NKUrhrGf9boLOb WWRgsI6eMZ2f6USU5DAA+tJs3t+AThIYd5mRP6nXlDysYSa1q9hHODMnr4VQgEqusj Yce7DgoEfgXXYsXvNccdy6CgHqIoEwGH5jX2raFKh+IVZxP76SEgXgIpOCgQ1MuXkO rG/zRSNZHBfwZKedeQ0XSNIAlFn8zJnr5BzCj295r6QeaFmQJDP/LnF3zzx+O0/Yvd oooLk9R+v6OiA== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sat, 17 Jan 2026 12:18:13 +0100 Message-Id: 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: <20260116214959.641032-4-ttabi@nvidia.com> Message-ID-Hash: RSREDP32EXAV2AKP32TLLUJRIIYZXSAH X-Message-ID-Hash: RSREDP32EXAV2AKP32TLLUJRIIYZXSAH X-MailFrom: dakr@kernel.org X-Mailman-Rule-Hits: nonmember-moderation X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation CC: Matthew Maurer , Gary Guo , Joel Fernandes , Alexandre Courbot , nouveau@lists.freedesktop.org, rust-for-linux@vger.kernel.org X-Mailman-Version: 3.3.8 Precedence: list List-Id: Nouveau development list Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: (Cc: Alice) Alice, for context, this is used when exporting a DMA buffer through debugf= s, while the DMA buffer may be in use by the device, i.e. no slice can be crea= ted. 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]) -> Result= { > 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 pointer= instead of a slice, > + /// along with a total buffer length, an offset into the that buffer= , 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 ass= ociated userspace slice > + /// even if it returns an error. > + /// > + /// # Safety > + /// > + /// - `data` must point to a valid memory region of at least `len` b= ytes that remains allocated > + /// for the duration of this call. > + /// > + /// Note: Unlike [`Self::write_slice`], this method does not require= 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 inconsistent= , 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 t= akes a dma::CoherentAllocation instead. Once we have generic I/O in place, t= his could be replaced with a generic write_io() method. 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 07420329E7D for ; Sat, 17 Jan 2026 11:18:16 +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=1768648697; cv=none; b=uaBWNARi8BPjV6QYvUDVo5+RYAVKbFLDH6b+DGQm2zHOb9eTFCyUo574Sy9utU1JE84sw+ReQEQFPo4DiK0G7pgzgsCqQ/XqGQgQdv0waFiaaeCKeOmjw6Lj4LB8+7UvZOJRYtYeifsG2eUouTn1ubZp9/ttcRJq/tOJreY0CIY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768648697; c=relaxed/simple; bh=r8pFE19enbEpY7dhMp0/C2AB6nWk5mDSkT6a80RWyqI=; h=Mime-Version:Content-Type:Date:Message-Id:To:From:Subject:Cc: References:In-Reply-To; b=kIly3vUDvCtyZ+Q3crVl95UrRSQ4+iayfp3eFzq64rek4zkj4JDtHBEp9k7+c5STzq8fDal/qR51n/3M2IQcrCch4qWjw+Lq5S6DzjCngDxWNhWgOHHPVKUW6STjvwC+mnott67ZaaFdL8fnnnMSYZi9rnOH8ThszefvzbgOjJY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=p4W5icmm; 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="p4W5icmm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0235CC4CEF7; Sat, 17 Jan 2026 11:18:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768648696; bh=r8pFE19enbEpY7dhMp0/C2AB6nWk5mDSkT6a80RWyqI=; h=Date:To:From:Subject:Cc:References:In-Reply-To:From; b=p4W5icmmAKGZxgj0llhic9EJcPcciAHWRUgg2ptPSvqsDsCEdphtvZcB2aL0CD4V1 hlXryIpiW8W3O77m/jBm+bG57x7ds0iv3npPjWknrv/l9a9xIvr1NKUrhrGf9boLOb WWRgsI6eMZ2f6USU5DAA+tJs3t+AThIYd5mRP6nXlDysYSa1q9hHODMnr4VQgEqusj Yce7DgoEfgXXYsXvNccdy6CgHqIoEwGH5jX2raFKh+IVZxP76SEgXgIpOCgQ1MuXkO rG/zRSNZHBfwZKedeQ0XSNIAlFn8zJnr5BzCj295r6QeaFmQJDP/LnF3zzx+O0/Yvd oooLk9R+v6OiA== 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 12:18:13 +0100 Message-Id: To: "Timur Tabi" From: "Danilo Krummrich" Subject: Re: [PATCH v5 3/8] rust: uaccess: add UserSliceWriter::write_buffer() for raw pointer writes Cc: "Matthew Maurer" , "Gary Guo" , "John Hubbard" , "Joel Fernandes" , "Alexandre Courbot" , , References: <20260116214959.641032-1-ttabi@nvidia.com> <20260116214959.641032-4-ttabi@nvidia.com> In-Reply-To: <20260116214959.641032-4-ttabi@nvidia.com> (Cc: Alice) Alice, for context, this is used when exporting a DMA buffer through debugf= s, while the DMA buffer may be in use by the device, i.e. no slice can be crea= ted. 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]) -> Result= { > 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 pointer= instead of a slice, > + /// along with a total buffer length, an offset into the that buffer= , 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 ass= ociated userspace slice > + /// even if it returns an error. > + /// > + /// # Safety > + /// > + /// - `data` must point to a valid memory region of at least `len` b= ytes that remains allocated > + /// for the duration of this call. > + /// > + /// Note: Unlike [`Self::write_slice`], this method does not require= 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 inconsistent= , 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 t= akes a dma::CoherentAllocation instead. Once we have generic I/O in place, t= his could be replaced with a generic write_io() method.