[PATCH v2 1/5] mm/hmm: HMM API to enable P2P DMA for device private pages

[Matthew Wilcox]

On Fri, Jul 18, 2025 at 02:51:08PM +0300, Yonatan Maman wrote:
> +++ b/include/linux/memremap.h
> @@ -89,6 +89,14 @@ struct dev_pagemap_ops {
>  	 */
>  	vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
>  
> +	/*
> +	 * Used for private (un-addressable) device memory only. Return a
> +	 * corresponding PFN for a page that can be mapped to device
> +	 * (e.g using dma_map_page)
> +	 */
> +	int (*get_dma_pfn_for_device)(struct page *private_page,
> +				      unsigned long *dma_pfn);

This makes no sense.  If a page is addressable then it has a PFN.
If a page is not addressable then it doesn't have a PFN.