linux-kernel - Re: [PATCH v5 04/14] driver core: platform: Add driver dma ownership management

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Message-ID: <20220214134303.GA929467@nvidia.com>
Date:   Mon, 14 Feb 2022 09:43:03 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christoph Hellwig <hch@...radead.org>,
        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 04/14] driver core: platform: Add driver dma ownership
 management

On Mon, Feb 14, 2022 at 02:37:15PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Feb 14, 2022 at 09:18:53AM -0400, Jason Gunthorpe wrote:
> > On Mon, Feb 14, 2022 at 10:59:50AM +0100, Greg Kroah-Hartman wrote:
> > 
> > > > +	if (ret && !drv->no_kernel_api_dma)
> > > > +		iommu_device_unuse_dma_api(dev);
> > > 
> > > So you are now going to call this for every platform driver _unless_
> > > they set this flag?
> > 
> > Yes, it is necessary because VFIO supports platform devices as well
> > and needs to ensure security. Conflicting kernel driver attachements
> > must be blocked, just like for PCI.
> 
> A platform device shouldn't be using VFIO, but ugh, oh well, that ship
> has sailed :(

I don't know why you say that, but yes, this is was set long ago.

> And stop it with the "security" mess, do not give people a false sense
> of it here please.

I'm confused by what you mean. This is all about what we tend to refer
to as DMA security - meaning a device's DMA can be controled by a
hostile environment and not impact the integrity of the kernel.

Jason