linux-kernel - Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

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Date:   Thu, 6 Jan 2022 11:43:25 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Christoph Hellwig <hch@...radead.org>
Cc:     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>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        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 v5 01/14] iommu: Add dma ownership management interfaces

Hi Bjorn,

On 1/5/22 12:41 AM, Bjorn Helgaas wrote:
>>> This adds dma ownership management in iommu core and exposes several
>>> interfaces for the device drivers and the device userspace assignment
>>> framework (i.e. vfio), so that any conflict between user and kernel
>>> controlled DMA could be detected at the beginning.
> Maybe I'm missing the point because I don't know what "conflict
> between user and kernel controlled DMA" is.  Are you talking about
> both userspace and the kernel programming the same device to do DMA?

It's about both userspace and kernel programming different devices
belonging to a same iommu group to do DMA. For example, PCI device A and
B sit in a some iommu group. Userspace programs device A for DMA and a
kernel driver programs device B. Userspace may intentionally or
unintentionally program device A to access and change device B's MMIO
with P2P DMA transactions which cause the kernel driver for device B
result in an inconsistent state.

This may not be all, just an example.

Best regards,
baolu