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Date:   Mon, 15 Nov 2021 05:21:26 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joerg Roedel <joro@8bytes.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
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        Ashok Raj <ashok.raj@intel.com>,
        Chaitanya Kulkarni <kch@nvidia.com>, kvm@vger.kernel.org,
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        Cornelia Huck <cohuck@redhat.com>,
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        Jacob jun Pan <jacob.jun.pan@intel.com>,
        Diana Craciun <diana.craciun@oss.nxp.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [PATCH 03/11] PCI: pci_stub: Suppress kernel DMA ownership
 auto-claiming
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On Mon, Nov 15, 2021 at 10:05:44AM +0800, Lu Baolu wrote:
> pci_stub allows the admin to block driver binding on a device and make
> it permanently shared with userspace. Since pci_stub does not do DMA,
> it is safe.

If an IOMMU is setup and dma-iommu or friends are not used nothing is
unsafe anyway, it just is that IOMMU won't work..

> However the admin must understand that using pci_stub allows
> userspace to attack whatever device it was bound to.

I don't understand this sentence at all.