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Date: Wed, 28 Jan 2026 11:53:48 +0100
Message-Id: <DG0607SU943F.1FDOPYPN38FCS@kernel.org>
Subject: Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC
 firmware parsing
Cc: <linux-kernel@vger.kernel.org>, "Paul Walmsley" <pjw@kernel.org>,
 "Palmer Dabbelt" <palmer@dabbelt.com>, "Albert Ou" <aou@eecs.berkeley.edu>,
 "Alexandre Ghiti" <alex@ghiti.fr>, "Miguel Ojeda" <ojeda@kernel.org>,
 "Boqun Feng" <boqun.feng@gmail.com>, "Gary Guo" <gary@garyguo.net>,
 =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, "Benno Lossin"
 <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Alice
 Ryhl" <aliceryhl@google.com>, "Trevor Gross" <tmgross@umich.edu>,
 "Alexandre Courbot" <acourbot@nvidia.com>, "John Hubbard"
 <jhubbard@nvidia.com>, "Alistair Popple" <apopple@nvidia.com>, "Timur Tabi"
 <ttabi@nvidia.com>, "Edwin Peer" <epeer@nvidia.com>, "Zhi Wang"
 <zhiw@nvidia.com>, "David Airlie" <airlied@gmail.com>, "Simona Vetter"
 <simona@ffwll.ch>, "Bjorn Helgaas" <bhelgaas@google.com>, "Alex Gaynor"
 <alex.gaynor@gmail.com>, "Dirk Behme" <dirk.behme@gmail.com>,
 <nouveau@lists.freedesktop.org>, <dri-devel@lists.freedesktop.org>,
 <rust-for-linux@vger.kernel.org>, <linux-riscv@lists.infradead.org>
To: "Joel Fernandes" <joelagnelf@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260126202305.2526618-1-joelagnelf@nvidia.com>
 <20260126202305.2526618-2-joelagnelf@nvidia.com>
In-Reply-To: <20260126202305.2526618-2-joelagnelf@nvidia.com>

On Mon Jan 26, 2026 at 9:23 PM CET, Joel Fernandes wrote:
> @@ -267,7 +264,12 @@ fn new_fwsec(dev: &Device<device::Bound>, bios: &Vbi=
os, cmd: FwsecCommand) -> Re
>          let ucode =3D bios.fwsec_image().ucode(&desc)?;
>          let mut dma_object =3D DmaObject::from_data(dev, ucode)?;
> =20
> -        let hdr_offset =3D usize::from_safe_cast(desc.imem_load_size() +=
 desc.interface_offset());
> +        // Compute hdr_offset =3D imem_load_size + interface_offset.

I do get the idea behind those comments, but are we sure that's really a go=
od
idea? How do we ensure to keep them up to date in case we have to change th=
e
code?

If we really want this, I'd at least chose a common syntax, e.g.

	// CALC: `imem_load_size + interface_offset`

without the variable name the resulting value is assigned to.

But I'd rather prefer to just drop those comments.

> +        let hdr_offset =3D desc
> +            .imem_load_size()
> +            .checked_add(desc.interface_offset())
> +            .map(usize::from_safe_cast)
> +            .ok_or(EINVAL)?;
>          // SAFETY: we have exclusive access to `dma_object`.
>          let hdr: &FalconAppifHdrV1 =3D unsafe { transmute(&dma_object, h=
dr_offset) }?;