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

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Message-Id: <DFYJMH9S9RHC.34AA6HRKPMC6X@garyguo.net>
Date: Mon, 26 Jan 2026 13:08:47 +0000
From: "Gary Guo" <gary@...yguo.net>
To: "John Hubbard" <jhubbard@...dia.com>, "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 Sat Jan 24, 2026 at 1:42 AM GMT, John Hubbard wrote:
> On 1/23/26 5:38 PM, John Hubbard wrote:
>> 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).
>>  
>> 
>
> Oh, forget to mention that I also changed it to use .as_slice(), so:
>
>      // 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).
>      let fmc_full_data = unsafe { fsp_fw.fmc_full.as_slice(0, fsp_fw.fmc_full.size())? };

If they're never submitted to hardware, why are they dma objects?

Best,
Gary