Re: [PATCH v5 07/14] PCI: Add driver dma ownership management - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.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>,
	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 v5 07/14] PCI: Add driver dma ownership management
Date: Mon, 14 Feb 2022 11:03:42 +0100	[thread overview]
Message-ID: <Ygoo/lCt/G6tWDz9@kroah.com> (raw)
In-Reply-To: <20220104015644.2294354-8-baolu.lu@linux.intel.com>

On Tue, Jan 04, 2022 at 09:56:37AM +0800, Lu Baolu wrote:
> Multiple PCI devices may be placed in the same IOMMU group because
> they cannot be isolated from each other. These devices must either be
> entirely under kernel control or userspace control, never a mixture. This
> checks and sets DMA ownership during driver binding, and release the
> ownership during driver unbinding.
> 
> The device driver may set a new flag (no_kernel_api_dma) to skip calling
> iommu_device_use_dma_api() during the binding process. For instance, the
> userspace framework drivers (vfio etc.) which need to manually claim
> their own dma ownership when assigning the device to userspace.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  include/linux/pci.h      |  5 +++++
>  drivers/pci/pci-driver.c | 21 +++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 18a75c8e615c..d29a990e3f02 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -882,6 +882,10 @@ struct module;
>   *              created once it is bound to the driver.
>   * @driver:	Driver model structure.
>   * @dynids:	List of dynamically added device IDs.
> + * @no_kernel_api_dma: Device driver doesn't use kernel DMA API for DMA.
> + *		Drivers which don't require DMA or want to manually claim the
> + *		owner type (e.g. userspace driver frameworks) could set this
> + *		flag.

Again with the bikeshedding, but this name is a bit odd.  Of course it's
in the kernel, this is all kernel code, so you can drop that.  And
again, "negative" flags are rough.  So maybe just "prevent_dma"?

thanks,

greg k-h
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