linux-kernel - Re: [PATCH v2 10/11] coco: arm64: dma: Update force_dma

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Message-ID: <20251120175807.00007c2e@huawei.com>
Date: Thu, 20 Nov 2025 17:58:07 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
CC: <linux-coco@...ts.linux.dev>, <kvmarm@...ts.linux.dev>,
	<linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<dan.j.williams@...el.com>, <aik@....com>, <lukas@...ner.de>, Samuel Ortiz
	<sameo@...osinc.com>, Xu Yilun <yilun.xu@...ux.intel.com>, Jason Gunthorpe
	<jgg@...pe.ca>, Suzuki K Poulose <Suzuki.Poulose@....com>, Steven Price
	<steven.price@....com>, Bjorn Helgaas <helgaas@...nel.org>, Catalin Marinas
	<catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>, Will Deacon
	<will@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>
Subject: Re: [PATCH v2 10/11] coco: arm64: dma: Update force_dma_unencrypted
 for accepted devices

On Mon, 17 Nov 2025 19:30:06 +0530
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org> wrote:

> This change updates the DMA behavior for accepted devices by assuming
> they access only private memory. Currently, the DMA API does not provide
> a mechanism for allocating shared memory that can be accessed by both
> the secure realm and the non-secure host.
> 
> Accepted devices are therefore expected to operate entirely within the
> private memory space. As of now, there is no API in the DMA layer that
> allows such devices to explicitly request shared memory allocations for
> coherent data exchange with the host.

Isn't this sentence a bit of a repeat of the one at the end of the
1st paragraph.

> 
> If future use cases require accepted devices to interact with shared
> memory— for example, for host-device communication, we will need to
> extend the DMA interface to support such allocation semantics. This
> commit lays the groundwork for that by clearly defining the current
> assumption and isolating the enforcement to force_dma_unencrypted.
> 
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@...nel.org>