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	Fri, 18 Jul 2025 14:17:00 +0000
Date: Fri, 18 Jul 2025 15:17:00 +0100
From: Matthew Wilcox <willy@infradead.org>
To: Yonatan Maman <ymaman@nvidia.com>
Cc: =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
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	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Alistair Popple <apopple@nvidia.com>,
	Ben Skeggs <bskeggs@nvidia.com>,
	Michael Guralnik <michaelgur@nvidia.com>,
	Or Har-Toov <ohartoov@nvidia.com>,
	Daisuke Matsuda <dskmtsd@gmail.com>, Shay Drory <shayd@nvidia.com>,
	linux-mm@kvack.org, linux-rdma@vger.kernel.org,
	dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, Gal Shalom <GalShalom@nvidia.com>
Subject: Re: [PATCH v2 1/5] mm/hmm: HMM API to enable P2P DMA for device
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References: <20250718115112.3881129-1-ymaman@nvidia.com>
 <20250718115112.3881129-2-ymaman@nvidia.com>
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In-Reply-To: <20250718115112.3881129-2-ymaman@nvidia.com>

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.