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

From: Bjorn Helgaas <helgaas@kernel.org>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Stuart Yoder <stuyoder@gmail.com>,
	rafael@kernel.org, David Airlie <airlied@linux.ie>,
	linux-pci@vger.kernel.org,
	Thierry Reding <thierry.reding@gmail.com>,
	Diana Craciun <diana.craciun@oss.nxp.com>,
	Dmitry Osipenko <digetx@gmail.com>, Will Deacon <will@kernel.org>,
	Ashok Raj <ashok.raj@intel.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Christoph Hellwig <hch@infradead.org>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	kvm@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Cornelia Huck <cohuck@redhat.com>,
	linux-kernel@vger.kernel.org, Li Yang <leoyang.li@nxp.com>,
	iommu@lists.linux-foundation.org,
	Jacob jun Pan <jacob.jun.pan@intel.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v4 03/13] PCI: pci_stub: Suppress kernel DMA ownership auto-claiming
Date: Wed, 29 Dec 2021 14:42:02 -0600	[thread overview]
Message-ID: <20211229204202.GA1700874@bhelgaas> (raw)
In-Reply-To: <20211217063708.1740334-4-baolu.lu@linux.intel.com>

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@linux.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
> 
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