linux-kernel - Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming

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Date:   Wed, 29 Dec 2021 14:42:02 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     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>,
        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 v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership
 auto-claiming

On Fri, Dec 17, 2021 at 02:36:58PM +0800, Lu Baolu wrote:
> The pci_dma_configure() marks the iommu_group as containing only devices
> with kernel drivers that manage DMA.

I'm looking at pci_dma_configure(), and I don't see the connection to
iommu_groups.

> Avoid this default behavior for the
> pci_stub because it does not program any DMA itself.  This allows the
> pci_stub still able to be used by the admin to block driver binding after
> applying the DMA ownership to vfio.

> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/pci/pci-stub.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/pci-stub.c b/drivers/pci/pci-stub.c
> index e408099fea52..6324c68602b4 100644
> --- a/drivers/pci/pci-stub.c
> +++ b/drivers/pci/pci-stub.c
> @@ -36,6 +36,9 @@ static struct pci_driver stub_driver = {
>  	.name		= "pci-stub",
>  	.id_table	= NULL,	/* only dynamic id's */
>  	.probe		= pci_stub_probe,
> +	.driver		= {
> +		.suppress_auto_claim_dma_owner = true,

The new .suppress_auto_claim_dma_owner controls whether we call
iommu_device_set_dma_owner().  I guess you added
.suppress_auto_claim_dma_owner because iommu_device_set_dma_owner()
must be done *before* we call the driver's .probe() method?

Otherwise, we could call some new interface from .probe() instead of
adding the flag to struct device_driver.

> +	},
>  };
>  
>  static int __init pci_stub_init(void)
> -- 
> 2.25.1
>