[PATCH v5] drm/nova: Align GEM memory allocation to system page size

[PATCH v5] 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

Changes in v5:
- Remove unnecessary variable declaration.
- Consolidate page_align call to use ok_or().and_then() for returned
  Result.

 drivers/gpu/drm/nova/gem.rs | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
index a07e922e25ef..e1b57609b8f7 100644
--- a/drivers/gpu/drm/nova/gem.rs
+++ b/drivers/gpu/drm/nova/gem.rs
@@ -3,10 +3,7 @@
 use kernel::{
     drm,
     drm::{gem, gem::BaseObject},
-    page::{
-        page_align,
-        PAGE_SIZE, //
-    },
+    page::page_align,
     prelude::*,
     sync::aref::ARef,
 };
@@ -31,14 +28,12 @@ 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>>> {
-        // Check for 0 size or potential usize overflow before calling page_align
-        if size == 0 || size > usize::MAX - PAGE_SIZE + 1 {
+        if size == 0 {
             return Err(EINVAL);
         }
-
-        let aligned_size = page_align(size);
-
-        gem::Object::new(dev, aligned_size)
+        page_align(size)
+            .ok_or(EINVAL)
+            .and_then(|size| gem::Object::new(dev, size))
     }
 
     /// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.

base-commit: b927546677c876e26eba308550207c2ddf812a43
prerequisite-patch-id: 7154ef17c3e40275152c90eff07bffcb5ef5e5cb
-- 
2.52.0

Re: [PATCH v5] drm/nova: Align GEM memory allocation to system page size

[Danilo Krummrich]

On Tue Dec 23, 2025 at 2:59 PM CET, Brendan Shephard wrote:
> diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
> index a07e922e25ef..e1b57609b8f7 100644
> --- a/drivers/gpu/drm/nova/gem.rs
> +++ b/drivers/gpu/drm/nova/gem.rs
> @@ -3,10 +3,7 @@
>  use kernel::{
>      drm,
>      drm::{gem, gem::BaseObject},
> -    page::{
> -        page_align,
> -        PAGE_SIZE, //
> -    },
> +    page::page_align,
>      prelude::*,
>      sync::aref::ARef,
>  };
> @@ -31,14 +28,12 @@ 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>>> {
> -        // Check for 0 size or potential usize overflow before calling page_align
> -        if size == 0 || size > usize::MAX - PAGE_SIZE + 1 {
> +        if size == 0 {
>              return Err(EINVAL);
>          }
> -
> -        let aligned_size = page_align(size);
> -
> -        gem::Object::new(dev, aligned_size)
> +        page_align(size)
> +            .ok_or(EINVAL)
> +            .and_then(|size| gem::Object::new(dev, size))
>      }
>  
>      /// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
>
> base-commit: b927546677c876e26eba308550207c2ddf812a43
> prerequisite-patch-id: 7154ef17c3e40275152c90eff07bffcb5ef5e5cb

This looks like this is an incremental patch on top of some previous version of
this one.

However, in this case I don't think there is a need to resend, since I prefer v4
over this one. Eventually we will need to use size (or aligned_size) outside of
the closure for further calculations.

I will pick up v4 of this patch, no need to resend, thanks!

Re: [PATCH v5] drm/nova: Align GEM memory allocation to system page size

[Brendan Shephard]

On Tue, Dec 23, 2025 at 09:11:36PM +0100, Danilo Krummrich wrote:
> On Tue Dec 23, 2025 at 2:59 PM CET, Brendan Shephard wrote:
> > @@ -31,14 +28,12 @@ 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>>> {
> > -        // Check for 0 size or potential usize overflow before calling page_align
> > -        if size == 0 || size > usize::MAX - PAGE_SIZE + 1 {
> > +        if size == 0 {
> >              return Err(EINVAL);
> >          }
> > -
> > -        let aligned_size = page_align(size);
> > -
> > -        gem::Object::new(dev, aligned_size)
> > +        page_align(size)
> > +            .ok_or(EINVAL)
> > +            .and_then(|size| gem::Object::new(dev, size))
> >      }
> >  
> >      /// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
> >
> > base-commit: b927546677c876e26eba308550207c2ddf812a43
> > prerequisite-patch-id: 7154ef17c3e40275152c90eff07bffcb5ef5e5cb
> 
> This looks like this is an incremental patch on top of some previous version of
> this one.
> 
> However, in this case I don't think there is a need to resend, since I prefer v4
> over this one. Eventually we will need to use size (or aligned_size) outside of
> the closure for further calculations.
> 
> I will pick up v4 of this patch, no need to resend, thanks!
> 

Hey Danilo,

Thanks, no worries, happy for you to take v4. I did build it
against your repo as well and there were no conflicts at the time. Just
the prereq patch to page_align and it was nice and clean.

Have a great holiday mate!

Brendan