linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Add opt-in for ATS support on discrete devices

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Message-ID: <Y/3yNaQD5Pkvf61k@nvidia.com>
Date:   Tue, 28 Feb 2023 08:23:17 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Add opt-in for ATS support on discrete
 devices

On Tue, Feb 28, 2023 at 10:33:41AM +0800, Lu Baolu wrote:
> In normal processing of PCIe ATS requests, the IOMMU performs address
> translation and returns the device a physical memory address which
> will be stored in that device's IOTLB. The device may subsequently
> issue Translated DMA request containing physical memory address. The
> IOMMU only checks that the device was allowed to issue such requests
> and does not attempt to validate the physical address.
> 
> The Intel IOMMU implementation only allows PCIe ATS on several SOC-
> integrated devices which are opt-in’ed through the ACPI tables to
> prevent any compromised device from accessing arbitrary physical
> memory.
> 
> Add a kernel option intel_iommu=relax_ats to allow users to have an
> opt-in to allow turning on ATS at as wish, especially for CSP-owned
> vertical devices. In any case, risky devices are not allowed to use
> ATS.

Why is this an intel specific option? all it does is effectively
disable untrusted? Why not a global option? All iommu with ATS will
need this?

Also, why doesn't a "CSP" set their ACPI to make the devices they want
to use ATS with trusted instead of this?

Jason