linux-kernel - Re: [PATCH 9/9] iommu/amd: Set default domain to IDENTITY

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Message-ID: <20240501141737.GB1723318@ziepe.ca>
Date: Wed, 1 May 2024 11:17:37 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, joro@...tes.org,
	thomas.lendacky@....com, vasant.hegde@....com, michael.roth@....com,
	jon.grimm@....com, rientjes@...gle.com
Subject: Re: [PATCH 9/9] iommu/amd: Set default domain to IDENTITY_DOMAIN
 when running in SEV guest

On Tue, Apr 30, 2024 at 03:24:30PM +0000, Suravee Suthikulpanit wrote:
> Since SEV guest depends on the unencrypted swiotlb bounce buffer
> to support DMA, the guest AMD IOMMU driver must be force to setup to
> pass-through mode.

You should block the creation of paging domains as well if the HW
can't support them.

But, is there actually a functional problem here? Doesn't swiotlb work
OK with iommu even with the encrypted memory cases? What is missing if
not?

Jason