linux-kernel - Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC firmware parsing

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Message-Id: <DG0NI832K0H5.25HYXTD205X7B@nvidia.com>
Date: Thu, 29 Jan 2026 09:36:38 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Danilo Krummrich" <dakr@...nel.org>
Cc: "Joel Fernandes" <joelagnelf@...dia.com>,
 <linux-kernel@...r.kernel.org>, "Paul Walmsley" <pjw@...nel.org>, "Palmer
 Dabbelt" <palmer@...belt.com>, "Albert Ou" <aou@...s.berkeley.edu>,
 "Alexandre Ghiti" <alex@...ti.fr>, "Miguel Ojeda" <ojeda@...nel.org>,
 "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Alistair
 Popple" <apopple@...dia.com>, "Zhi Wang" <zhiw@...dia.com>, "Simona Vetter"
 <simona@...ll.ch>, "Bjorn Helgaas" <bhelgaas@...gle.com>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Dirk Behme" <dirk.behme@...il.com>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
 <rust-for-linux@...r.kernel.org>, <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC
 firmware parsing

On Thu Jan 29, 2026 at 9:20 AM JST, Danilo Krummrich wrote:
> On Wed Jan 28, 2026 at 4:14 PM CET, Joel Fernandes wrote:
>> On 1/28/2026 5:53 AM, Danilo Krummrich wrote:
>>> 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: &Vbios, cmd: FwsecCommand) -> Re
>>>>           let ucode = bios.fwsec_image().ucode(&desc)?;
>>>>           let mut dma_object = DmaObject::from_data(dev, ucode)?;
>>>>   
>>>> -        let hdr_offset = usize::from_safe_cast(desc.imem_load_size() + desc.interface_offset());
>>>> +        // Compute hdr_offset = imem_load_size + interface_offset.
>>> 
>>> I do get the idea behind those comments, but are we sure that's really a good
>>> idea? How do we ensure to keep them up to date in case we have to change the
>>> 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.
>> The idea of adding these comments was to improve readability. However, I 
>> can drop them in the v3, that's fine with me.
>
> Yeah, that's why I wrote "I get the idea". :) But as I write above, I'm
> concerned about the comments getting outdated or inconsistent over time.
>
> Besides that, it more seems like something your favorite editor should help with
> instead.
>
>> Do you want me to wait for additional comments on this series, or should 
>> I make the update and repost it?  Thanks,
>
> As mentioned, I tend to think we should just drop them, but I'm happy to hear
> some more opinions on this if any.

For safety I would keep something like the 

  // CALC: `imem_load_size + interface_offset`

you suggested. From simple operations yes, the code would be obvious,
but there are also more involved computations where order matters and it
is good to have a reference. These shouldn't change often anyway, and
the `CALC:` header catches the attention of anyone who would update
them, similarly to a `SAFETY:` comment.

If Joel agrees, I will amend the comments accordingly in my staging
branch.