linux-kernel - Re: [PATCH 4/5] iommu/vt-d: Add support for static identity domain

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Date:   Wed, 29 Nov 2023 16:26:15 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] iommu/vt-d: Add support for static identity domain

On Mon, Nov 20, 2023 at 07:29:43PM +0800, Lu Baolu wrote:

> @@ -2311,6 +2316,13 @@ static int device_def_domain_type(struct device *dev)
>  			return IOMMU_DOMAIN_IDENTITY;
>  	}
>  
> +	/*
> +	 * Hardware does not support the passthrough translation mode.
> +	 * Always use a dynamaic mapping domain.
> +	 */
> +	if (!ecap_pass_through(iommu->ecap))
> +		return IOMMU_DOMAIN_DMA;
> +

Doesn't this return from def_domain_type completely prevent using an
identity domain?

I thought the point of this was to allow the identity domain but have
it be translating?

Jason