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

From: "Alexandre Courbot" <acourbot@nvidia.com>
To: "Danilo Krummrich" <dakr@kernel.org>
Cc: "Joel Fernandes" <joelagnelf@nvidia.com>,
	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>,
	"Björn 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>,
	"Alistair Popple" <apopple@nvidia.com>,
	"Zhi Wang" <zhiw@nvidia.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
Subject: Re: [PATCH v2 1/5] gpu: nova-core: use checked arithmetic in FWSEC firmware parsing
Date: Thu, 29 Jan 2026 09:36:38 +0900	[thread overview]
Message-ID: <DG0NI832K0H5.25HYXTD205X7B@nvidia.com> (raw)
In-Reply-To: <DG0N5PNS1ZQ0.13WMT4XYDXNUS@kernel.org>

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.

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