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
