linux-kernel - Re: [PATCH v3 2/4] gpu: nova-core: gsp: fix length of received messages

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Message-Id: <DEZHBXNOIVH4.2WIQRYI9W8P6P@nvidia.com>
Date: Tue, 16 Dec 2025 16:57:40 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "Alistair Popple" <apopple@...dia.com>, "Alexandre Courbot"
 <acourbot@...dia.com>
Cc: "Danilo Krummrich" <dakr@...nel.org>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Simona Vetter" <simona@...ll.ch>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "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>, "Trevor
 Gross" <tmgross@...ch.edu>, "Joel Fernandes" <joelagnelf@...dia.com>,
 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] gpu: nova-core: gsp: fix length of received
 messages

On Tue Dec 16, 2025 at 3:14 PM JST, Alistair Popple wrote:
> On 2025-12-16 at 13:57 +1100, Alexandre Courbot <acourbot@...dia.com> wrote...
>> The size of messages' payload is miscalculated, leading to extra data
>> passed to the message handler. While this is not a problem with our
>> current set of commands, others with a variable-length payload may
>> misbehave. Fix this by introducing a method returning the payload size
>> and using it.
>
> The whole inconsistency of the message element struct not including it's header
> fields in the size whilst the rpc struct does has caused endless confusion, this
> looks much better, thanks for fixing!

Indeed. It would be so much simpler if the RPC header just included the
size of its *payload* - because if we have the header to begin with, of
course it is part of the message!

Instead we have to deal with the possibility of a nonsensical length
value if it is shorter than that of the header. Thankfully a saturating
sub always yields a correct behavior, else we would have to return a
`Result`. :/

>
> Reviewed-by: Alistair Popple <apopple@...dia.com>

Thanks!