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

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

[Brendan Shephard]

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)?;
 
         gem::Object::new(dev, aligned_size)
     }

base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
-- 
2.51.1

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

[Alexandre Courbot]

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))

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

[Brendan Shephard]

On Thu, Dec 18, 2025 at 10:16:48PM +0900, Alexandre Courbot wrote:
> On Mon Dec 15, 2025 at 5:34 PM JST, Brendan Shephard 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 {
> > +        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))
> 

Sounds good, I'll use `and_then`. I like the idea of not unnecessarily
assigning variables just to use them once. I'll make that change, re-test
and send a new revision of this one.

Thanks!

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

[Danilo Krummrich]

On Mon Dec 15, 2025 at 9:34 AM CET, 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>

Applied to drm-rust-next, thanks!

    [ Import page module only. - Danilo ]

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