linux-kernel - Re: [PATCH] mm/hmm: Allow hmm_dma_map

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Message-ID: <aDCKsK2-zRkqge64@infradead.org>
Date: Fri, 23 May 2025 07:48:16 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Daisuke Matsuda <dskmtsd@...il.com>
Cc: linux-rdma@...r.kernel.org, linux-mm@...ck.org, leon@...nel.org,
	jgg@...pe.ca, akpm@...ux-foundation.org, jglisse@...hat.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	zyjzyj2000@...il.com
Subject: Re: [PATCH] mm/hmm: Allow hmm_dma_map_alloc() to tolerate NULL device

On Fri, May 23, 2025 at 02:35:37PM +0000, Daisuke Matsuda wrote:
> Some drivers (such as rxe) may legitimately call hmm_dma_map_alloc() with a
> NULL device pointer,

No, they may not.  If something has no device with physical DMA
capabilities, it has not business calling into it.