Re: [PATCH 3/4] drm/pagemap: Add helper to access zone_device_data

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Dec 16, 2025 at 09:10:13PM +0100, Francois Dugast wrote:
> This new helper helps ensure all accesses to zone_device_data use the
> correct API whether the page is part of a folio or not.
> 
> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Francois Dugast <francois.dugast@intel.com>
> ---
>  drivers/gpu/drm/drm_gpusvm.c  |  7 +++++--
>  drivers/gpu/drm/drm_pagemap.c | 32 +++++++++++++++++++++++++-------
>  include/drm/drm_pagemap.h     |  2 ++
>  3 files changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index 39c8c50401dd..d0ff6b65e543 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -1366,12 +1366,15 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
>  		order = drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages);
>  		if (is_device_private_page(page) ||
>  		    is_device_coherent_page(page)) {
> +			struct drm_pagemap_zdd *__zdd =
> +				drm_pagemap_page_zone_device_data(page);
> +
>  			if (!ctx->allow_mixed &&
> -			    zdd != page->zone_device_data && i > 0) {
> +			    zdd != __zdd && i > 0) {
>  				err = -EOPNOTSUPP;
>  				goto err_unmap;
>  			}
> -			zdd = page->zone_device_data;
> +			zdd = __zdd;
>  			if (pagemap != page_pgmap(page)) {
>  				if (i > 0) {
>  					err = -EOPNOTSUPP;
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 491de9275add..b71e47136112 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -192,6 +192,22 @@ static void drm_pagemap_migration_unlock_put_pages(unsigned long npages,
>  	}
>  }
>  
> +/**
> + * drm_pagemap_page_zone_device_data() - Page to zone_device_data
> + * @page: Pointer to the page
> + *
> + * Return: Page's zone_device_data
> + */
> +void *drm_pagemap_page_zone_device_data(struct page *page)
> +{
> +	struct folio *folio = page_folio(page);
> +

I think we can actually just do:

return folio_zone_device_data(folio)

We still need the helper as if page is part of a folio the individual
page->zone_device_data could be NULL.

Also since this called from GPU SVM maybe make this an inline in
drm_pagemap.h too. We'd have to include 'linux/memremap.h' in
drm_pagemap.h but I don't that is a huge deal. 

Matt

> +	if (folio_order(folio))
> +		return folio_zone_device_data(folio);
> +
> +	return page->zone_device_data;
> +}
> +
>  /**
>   * drm_pagemap_get_devmem_page() - Get a reference to a device memory page
>   * @page: Pointer to the page
> @@ -481,8 +497,8 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas,
>  			goto next;
>  
>  		if (fault_page) {
> -			if (src_page->zone_device_data !=
> -			    fault_page->zone_device_data)
> +			if (drm_pagemap_page_zone_device_data(src_page) !=
> +			    drm_pagemap_page_zone_device_data(fault_page))
>  				goto next;
>  		}
>  
> @@ -670,7 +686,7 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
>  	int i, err = 0;
>  
>  	if (page) {
> -		zdd = page->zone_device_data;
> +		zdd = drm_pagemap_page_zone_device_data(page);
>  		if (time_before64(get_jiffies_64(),
>  				  zdd->devmem_allocation->timeslice_expiration))
>  			return 0;
> @@ -722,7 +738,7 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
>  		if (!page)
>  			goto err_finalize;
>  	}
> -	zdd = page->zone_device_data;
> +	zdd = drm_pagemap_page_zone_device_data(page);
>  	ops = zdd->devmem_allocation->ops;
>  	dev = zdd->devmem_allocation->dev;
>  
> @@ -768,7 +784,9 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
>   */
>  static void drm_pagemap_folio_free(struct folio *folio)
>  {
> -	drm_pagemap_zdd_put(folio->page.zone_device_data);
> +	struct page *page = folio_page(folio, 0);
> +
> +	drm_pagemap_zdd_put(drm_pagemap_page_zone_device_data(page));
>  }
>  
>  /**
> @@ -784,7 +802,7 @@ static void drm_pagemap_folio_free(struct folio *folio)
>   */
>  static vm_fault_t drm_pagemap_migrate_to_ram(struct vm_fault *vmf)
>  {
> -	struct drm_pagemap_zdd *zdd = vmf->page->zone_device_data;
> +	struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(vmf->page);
>  	int err;
>  
>  	err = __drm_pagemap_migrate_to_ram(vmf->vma,
> @@ -847,7 +865,7 @@ EXPORT_SYMBOL_GPL(drm_pagemap_devmem_init);
>   */
>  struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page)
>  {
> -	struct drm_pagemap_zdd *zdd = page->zone_device_data;
> +	struct drm_pagemap_zdd *zdd = drm_pagemap_page_zone_device_data(page);
>  
>  	return zdd->devmem_allocation->dpagemap;
>  }
> diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
> index f6e7e234c089..3a8d0e1cef43 100644
> --- a/include/drm/drm_pagemap.h
> +++ b/include/drm/drm_pagemap.h
> @@ -245,4 +245,6 @@ int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
>  			    struct mm_struct *mm,
>  			    unsigned long timeslice_ms);
>  
> +void *drm_pagemap_page_zone_device_data(struct page *page);
> +
>  #endif
> -- 
> 2.43.0
>