linux-kernel - Re: [PATCH 29/31] gpu: nova-core: Hopper/Blackwell: add FSP Chain of Trust boot path

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Message-ID: <01b59562-9d90-459a-905d-56de1bc05433@nvidia.com>
Date: Fri, 23 Jan 2026 17:38:28 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Gary Guo <gary@...yguo.net>, Danilo Krummrich <dakr@...nel.org>
Cc: Alexandre Courbot <acourbot@...dia.com>,
 Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>,
 Alistair Popple <apopple@...dia.com>, Edwin Peer <epeer@...dia.com>,
 Zhi Wang <zhiw@...dia.com>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, 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>, nouveau@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 29/31] gpu: nova-core: Hopper/Blackwell: add FSP Chain of
 Trust boot path

On 1/21/26 8:35 AM, Gary Guo wrote:
> On Wed Dec 3, 2025 at 5:59 AM GMT, John Hubbard wrote:
...
>> +        // SAFETY: fmc_full is a valid DmaObject with a contiguous allocation of size() bytes
>> +        // starting at start_ptr(). The slice is only used for signature extraction within this
>> +        // function scope while fsp_fw remains valid.
>> +        let fmc_full_data = unsafe {
>> +            core::slice::from_raw_parts(fsp_fw.fmc_full.start_ptr(), fsp_fw.fmc_full.size())
>> +        };
> 
> The justification is week because it does not mention about the non-race nature
> of this, which need to be justified for a DMA allocation. If you use
> `CoherentAllocation::as_slice`, then this requirement would be obvious.
> 
> For example:
> 
>     // SAFETY: the dma buffer is not yet submitted too hardware and we are the
>     // unique owner at this point.
>     let fmc_full_data = unsafe { fsp_fw.fmc_full.as_slice(0, fsp_fw.fmc_full.size()) };
 
I see. OK, after a lot of fussing over the wording, I'm have come up
with this, which might be much too wordy? I'm not sure.

    // SAFETY: fmc_full, which contains the complete FMC ELF file, is never submitted to
    // hardware, so it is safe from hardware-software races. And we are the unique owner of
    // fsp_fw (and therefore of fsp_fw.fmc_full). (A separate buffer, fsp_fw.fmc_image, is what
    // gets submitted to the hardware).
 

thanks,
-- 
John Hubbard