linux-kernel - Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user

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Date:   Wed, 29 Sep 2021 09:59:02 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: Re: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma
 interfaces

On Wed, Sep 29, 2021 at 12:38:35AM +0000, Tian, Kevin wrote:

> /* If set the driver must call iommu_XX as the first action in probe() or
>   * before it attempts to do DMA
>   */
>  bool suppress_dma_owner:1;

It is not "attempts to do DMA" but more "operates the physical device
in any away"

Not having ownership means another entity could be using user space
DMA to manipulate the device state and attack the integrity of the
kernel's programming of the device.

Jason