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

[Alice Ryhl <aliceryhl@google.com>]

On Fri, Nov 21, 2025 at 02:04:28PM +1000, bshephar@bne-home.net wrote:
> Use page::page_align for GEM object memory allocation to ensure the
> allocation is page aligned. This ensures that the allocation is page
> aligned with the system in cases where 4096 is not the default.
> For example on 16k or 64k aarch64 systems this allocation should be
> aligned accordingly.
> 
> Signed-off-by: Brendan Shephard <bshephar@bne-home.net>
> ---
>  drivers/gpu/drm/nova/gem.rs | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
> index 2760ba4f3450..a07e922e25ef 100644
> --- a/drivers/gpu/drm/nova/gem.rs
> +++ b/drivers/gpu/drm/nova/gem.rs
> @@ -3,6 +3,10 @@
>  use kernel::{
>      drm,
>      drm::{gem, gem::BaseObject},
> +    page::{
> +        page_align,
> +        PAGE_SIZE, //
> +    },
>      prelude::*,
>      sync::aref::ARef,
>  };
> @@ -27,12 +31,13 @@ fn new(_dev: &NovaDevice, _size: usize) -> impl PinInit<Self, Error> {
>  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

>              return Err(EINVAL);
>          }
> 
> +        let aligned_size = page_align(size);
> +
>          gem::Object::new(dev, aligned_size)
>      }
> 
> --