[PATCH v2 2/3] drm/pagemap: Add a populate_mm op

[Matthew Brost]

On Wed, Jun 04, 2025 at 11:35:35AM +0200, Thomas Hellström wrote:
> Add an operation to populate a part of a drm_mm with device
> private memory.
> 

With the kernel doc fixed:
Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_gpusvm.c  |  7 ++-----
>  drivers/gpu/drm/drm_pagemap.c | 34 ++++++++++++++++++++++++++++++++++
>  include/drm/drm_pagemap.h     | 34 ++++++++++++++++++++++++++++++++++
>  3 files changed, 70 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index ef81381609de..51afc8a9704d 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -175,11 +175,8 @@
>   *		}
>   *
>   *		if (driver_migration_policy(range)) {
> - *			mmap_read_lock(mm);
> - *			devmem = driver_alloc_devmem();
> - *			err = drm_pagemap_migrate_to_devmem(devmem, gpusvm->mm, gpuva_start,
> - *                                                          gpuva_end, driver_pgmap_owner());
> - *                      mmap_read_unlock(mm);
> + *			err = drm_pagemap_populate_mm(driver_choose_drm_pagemap(),
> + *                                                    gpuva_start, gpuva_end, gpusvm->mm);
>   *			if (err)	// CPU mappings may have changed
>   *				goto retry;
>   *		}
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 3551a50d7381..25395685a9b8 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -6,6 +6,7 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/migrate.h>
>  #include <linux/pagemap.h>
> +#include <drm/drm_drv.h>
>  #include <drm/drm_pagemap.h>
>  
>  /**
> @@ -809,3 +810,36 @@ struct drm_pagemap *drm_pagemap_page_to_dpagemap(struct page *page)
>  	return zdd->devmem_allocation->dpagemap;
>  }
>  EXPORT_SYMBOL_GPL(drm_pagemap_page_to_dpagemap);
> +
> +/**
> + * drm_pagemap_populate_mm() - Populate a virtual range with device memory pages
> + * @dpagemap: Pointer to the drm_pagemap managing the device memory
> + * @start: Start of the virtual range to populate.
> + * @end: End of the virtual range to populate.
> + * @mm: Pointer to the virtual address space.
> + *
> + * Attempt to populate a virtual range with device memory pages,
> + * clearing them or migrating data from the existing pages if necessary.
> + * The function is best effort only, and implementations may vary
> + * in how hard they try to satisfy the request.
> + *
> + * Return: 0 on success, negative error code on error. If the hardware
> + * device was removed / unbound the function will return -ENODEV;
> + */
> +int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
> +			    unsigned long start, unsigned long end,
> +			    struct mm_struct *mm,
> +			    unsigned long timeslice_ms)
> +{
> +	int err;
> +
> +	if (!mmget_not_zero(mm))
> +		return -EFAULT;
> +	mmap_read_lock(mm);
> +	err = dpagemap->ops->populate_mm(dpagemap, start, end, mm,
> +					 timeslice_ms);
> +	mmap_read_unlock(mm);
> +	mmput(mm);
> +
> +	return err;
> +}
> diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
> index dabc9c365df4..e5f20a1235be 100644
> --- a/include/drm/drm_pagemap.h
> +++ b/include/drm/drm_pagemap.h
> @@ -92,6 +92,35 @@ struct drm_pagemap_ops {
>  			     struct device *dev,
>  			     struct drm_pagemap_device_addr addr);
>  
> +	/**
> +	 * @populate_mm: Populate part of the mm with @dpagemap memory,
> +	 * migrating existing data.
> +	 * @dpagemap: The struct drm_pagemap managing the memory.
> +	 * @start: The virtual start address in @mm
> +	 * @end: The virtual end address in @mm
> +	 * @mm: Pointer to a live mm. The caller must have an mmget()
> +	 * reference.
> +	 *
> +	 * The caller will have the mm lock at least in read mode.
> +	 * Note that there is no guarantee that the memory is resident
> +	 * after the function returns, it's best effort only.
> +	 * When the mm is not using the memory anymore,
> +	 * it will be released. The struct drm_pagemap might have a
> +	 * mechanism in place to reclaim the memory and the data will
> +	 * then be migrated. Typically to system memory.
> +	 * The implementation should hold sufficient runtime power-
> +	 * references while pages are used in an address space and
> +	 * should ideally guard against hardware device unbind in
> +	 * a way such that device pages are migrated back to system
> +	 * followed by device page removal. The implementation should
> +	 * return -ENODEV after device removal.
> +	 *
> +	 * Return: 0 if successful. Negative error code on error.
> +	 */
> +	int (*populate_mm)(struct drm_pagemap *dpagemap,
> +			   unsigned long start, unsigned long end,
> +			   struct mm_struct *mm,
> +			   unsigned long timeslice_ms);
>  };
>  
>  /**
> @@ -205,4 +234,9 @@ void drm_pagemap_devmem_init(struct drm_pagemap_devmem *devmem_allocation,
>  			     const struct drm_pagemap_devmem_ops *ops,
>  			     struct drm_pagemap *dpagemap, size_t size);
>  
> +int drm_pagemap_populate_mm(struct drm_pagemap *dpagemap,
> +			    unsigned long start, unsigned long end,
> +			    struct mm_struct *mm,
> +			    unsigned long timeslice_ms);
> +
>  #endif
> -- 
> 2.49.0
>