Re: [PATCH v7 05/11] PCI: pci_stub: Set driver_managed_dma

From: Bjorn Helgaas <helgaas@kernel.org>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joerg Roedel <joro@8bytes.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Christoph Hellwig <hch@infradead.org>,
	Kevin Tian <kevin.tian@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	kvm@vger.kernel.org, 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>,
	Stuart Yoder <stuyoder@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Chaitanya Kulkarni <kch@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>,
	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 v7 05/11] PCI: pci_stub: Set driver_managed_dma
Date: Mon, 28 Feb 2022 13:54:18 -0600	[thread overview]
Message-ID: <20220228195418.GA515725@bhelgaas> (raw)
In-Reply-To: <20220228005056.599595-6-baolu.lu@linux.intel.com>

On Mon, Feb 28, 2022 at 08:50:50AM +0800, Lu Baolu wrote:
> The current VFIO implementation allows pci-stub driver to be bound to
> a PCI device with other devices in the same IOMMU group being assigned
> to userspace. The pci-stub driver has no dependencies on DMA or the
> IOVA mapping of the device, but it does prevent the user from having
> direct access to the device, which is useful in some circumstances.
> 
> The pci_dma_configure() marks the iommu_group as containing only devices
> with kernel drivers that manage DMA. For compatibility with the VFIO
> usage, avoid this default behavior for the pci_stub. 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>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/pci-stub.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/pci-stub.c b/drivers/pci/pci-stub.c
> index e408099fea52..d1f4c1ce7bd1 100644
> --- a/drivers/pci/pci-stub.c
> +++ b/drivers/pci/pci-stub.c
> @@ -36,6 +36,7 @@ static struct pci_driver stub_driver = {
>  	.name		= "pci-stub",
>  	.id_table	= NULL,	/* only dynamic id's */
>  	.probe		= pci_stub_probe,
> +	.driver_managed_dma = true,
>  };
>  
>  static int __init pci_stub_init(void)
> -- 
> 2.25.1
> 
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