Re: [PATCH 1/1] drm: nova: Align GEM memory allocation to system page size

[Brendan Shephard <bshephar@bne-home.net>]

On Tue, Nov 25, 2025 at 09:23:59AM +0000, Alice Ryhl wrote:
> On Fri, Nov 21, 2025 at 02:04:28PM +1000, bshephar@bne-home.net wrote:
> >  impl NovaObject {
> >      /// Create a new DRM GEM object.
> >      pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result<ARef<gem::Object<Self>>> {
> > -        let aligned_size = size.next_multiple_of(1 << 12);
> > -
> > -        if size == 0 || size > aligned_size {
> > +        // Check for 0 size or potential usize overflow before calling page_align
> > +        if size == 0 || size > usize::MAX - PAGE_SIZE + 1 {
> 
> Maybe this should use isize::MAX as the maximum size instead? That's a
> pretty common maximum size for allocations in Rust and big enough for
> everyone.
> 
> Alice

Thanks for the review Alice. I used usize here because the page_align()
function specifically mentions that the provided value should not
overflow a ['usize'].
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/rust/kernel/page.rs#n30

I don't think that alone needs to be the deciding factor, but it's worth
expressing why I made that decision to begin with. Happy to hear your
thoughts, and if you still feel isize::MAX is more appropriate given
this information.

Brendan