linux-kernel - Re: [PATCH v8 04/11] bus: platform,amba,fsl-mc,PCI: Add device DMA ownership management

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Message-ID: <400b2dd3-120b-9728-3990-801b53447a2b@arm.com>
Date:   Tue, 8 Mar 2022 13:39:51 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>
Cc:     Will Deacon <will@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/11] bus: platform,amba,fsl-mc,PCI: Add device DMA
 ownership management

On 2022-03-08 05:44, Lu Baolu wrote:
> The devices on platform/amba/fsl-mc/PCI buses could be bound to drivers
> with the device DMA managed by kernel drivers or user-space applications.
> Unfortunately, multiple devices may be placed in the same IOMMU group
> because they cannot be isolated from each other. The DMA on these devices
> must either be entirely under kernel control or userspace control, never
> a mixture. Otherwise the driver integrity is not guaranteed because they
> could access each other through the peer-to-peer accesses which by-pass
> the IOMMU protection.
> 
> This checks and sets the default DMA mode during driver binding, and
> cleanups during driver unbinding. In the default mode, the device DMA is
> managed by the device driver which handles DMA operations through the
> kernel DMA APIs (see Documentation/core-api/dma-api.rst).
> 
> For cases where the devices are assigned for userspace control through the
> userspace driver framework(i.e. VFIO), the drivers(for example, vfio_pci/
> vfio_platfrom etc.) may set a new flag (driver_managed_dma) to skip this
> default setting in the assumption that the drivers know what they are
> doing with the device DMA.
> 
> Calling iommu_device_use_default_domain() before {of,acpi}_dma_configure
> is currently a problem. As things stand, the IOMMU driver ignored the
> initial iommu_probe_device() call when the device was added, since at
> that point it had no fwspec yet. In this situation,
> {of,acpi}_iommu_configure() are retriggering iommu_probe_device() after
> the IOMMU driver has seen the firmware data via .of_xlate to learn that
> it actually responsible for the given device. As the result, before
> that gets fixed, iommu_use_default_domain() goes at the end, and calls
> arch_teardown_dma_ops() if it fails.
> 
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Stuart Yoder <stuyoder@...il.com>
> Cc: Laurentiu Tudor <laurentiu.tudor@....com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Reviewed-by: Robin Murphy <robin.murphy@....com>