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

[Bjorn Helgaas]

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@xxxxxxxxxxxxxxx>
> ---
>  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
>