Re: [PATCH 10/11] gpu: nova-core: LibosMemoryRegionInitArgument size must be page aligned

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Dec 03, 2025 at 08:54:31PM +0900, Alexandre Courbot wrote:
> On Tue Dec 2, 2025 at 8:25 AM JST, Timur Tabi wrote:
> > On Wed, 2025-11-19 at 12:36 +0900, Alexandre Courbot wrote:
> >> You can use the `Alignment` type here, as the rest of the code does:
> >> 
> >>     let size = num::usize_as_u64(obj.size())
> >>         .align_up(Alignment::new::<GSP_PAGE_SIZE>())?;
> >> 
> >> Now `align_up` returns an error in case of overflow, that we will need
> >> to pass down to the caller by changing the return type of `new`. It is a
> >> bit annoying, but better than the behavior of `next_mutiple_of` in such
> >> a case, which is to panic. :)
> >
> > I see your point, but these are u64s that we're talking about.  The only way next_mutiple_of() can
> > panic is if obj.size() is greater than 0xFFFFFFFFFFFFF000, which is not possible.  
> >
> > I would say in this case, a panic is preferable to a convoluted error return that will never be
> > exercised, because failure here indicates a coding error, not an input error.
> 
> The input data is a usize, so technically we could get an input that
> triggers that error.
> 
> I know it's a very edge case, and clearly indicates a bug, but the
> general rule is: don't panic the kernel. And in Rust, if possible, don't
> even let me compiler insert panic-handling code. If you don't want to
> change the return type of the method, then maybe use `unwrap_or` and
> `inspect_err` to print an error before returning e.g. `0`.
> 
> But others have already thought "naah, that's never gonna happen" and
> got burnt very publicly [1], so let's learn from that. :P
> 
> [1] https://blog.cloudflare.com/18-november-2025-outage/

For what it's worth, my friend at Cloudflare tells me they would have
failed in the same way had they used ? instead of unwrap.

Alice