Re: [PATCH v4] drm/nova: Align GEM memory allocation to system page size

["Alexandre Courbot" <acourbot@nvidia.com>]

On Mon Dec 15, 2025 at 5:34 PM JST, Brendan Shephard wrote:
> Use page::page_align for GEM object memory allocation to ensure the
> allocation is page aligned. This is important on systems where the
> default page size is not 4k. Such as 16k or 64k aarch64 systems.
>
> This change uses the updated page_align() function which returns
> Option<usize> for overflow safety. (See "rust: Return Option from
> page_align and ensure no usize overflow").
>
> Signed-off-by: Brendan Shephard <bshephar@bne-home.net>
> ---
> Changes in v2:
> - Updated to use the new page_align() Option<usize> return value
> - Prerequisite patch:
>   https://lore.kernel.org/rust-for-linux/20251204224006.353646-2-bshephar@bne-home.net/T/#u
> - Link to v1: https://lore.kernel.org/rust-for-linux/98227EBD-92F7-40FC-A5A4-3FF3780FB2CB@bne-home.net/
>
> Changes in v3:
> - Add back missing semi-colon after ok_or().
> - Reword commit message to be more concise.
> - Link to v2: https://lore.kernel.org/rust-for-linux/20251208064405.573026-1-bshephar@bne-home.net/T/#u
>
> Changes in v4:
> - Add back the size == 0 check;
> - Rebase on latest drm-next branch
> - Link to v3: https://lore.kernel.org/rust-for-linux/20251208071810.653223-1-bshephar@bne-home.net/T/#u
>
>  drivers/gpu/drm/nova/gem.rs | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
> index 2760ba4f3450..3a3a41e8d4bc 100644
> --- a/drivers/gpu/drm/nova/gem.rs
> +++ b/drivers/gpu/drm/nova/gem.rs
> @@ -3,6 +3,7 @@
>  use kernel::{
>      drm,
>      drm::{gem, gem::BaseObject},
> +    page::page_align,
>      prelude::*,
>      sync::aref::ARef,
>  };
> @@ -27,11 +28,10 @@ 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 {
> +        if size == 0 {
>              return Err(EINVAL);
>          }
> +        let aligned_size = page_align(size).ok_or(EINVAL)?;

nit, but it's a good practice to always leave an empty line before a
block of variable declarations.

>  
>          gem::Object::new(dev, aligned_size)

... or if you prefer to avoid the variable altogether:

    page_align(size)
        .ok_or(EINVAL)
        .and_then(|size| gem::Object::new(dev, size))