linux-kernel - Re: [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach

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Date:   Mon, 14 Feb 2022 14:40:56 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        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 v1 5/8] iommu/amd: Use iommu_attach/detach_device()

On Mon, Feb 14, 2022 at 09:15:44AM -0400, Jason Gunthorpe wrote:
> But how does the sound device know that this has been done to it?
> 
> eg how do we know the sound device hasn't been bound to VFIO or
> something at this point?

The iommu_attach_group() call will fail when the group (which includes
GPU and sound device) it not in its default-domain. So if VFIO attached
the group to its own domain, there is a failure in this init function.

Note that this function is intended to be called by the driver currently
controling this device, so there should also be no race with VFIO trying
to grab the device in parallel.

Regards,

	Joerg