Re: [PATCH v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups

From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org>
To: Joerg Roedel <joro@8bytes.org>
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>,
	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 v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups
Date: Tue, 15 Feb 2022 09:47:44 -0400	[thread overview]
Message-ID: <20220215134744.GO4160@nvidia.com> (raw)
In-Reply-To: <YgtrJVI9wGMFdPWk@8bytes.org>

On Tue, Feb 15, 2022 at 09:58:13AM +0100, Joerg Roedel wrote:
> On Mon, Feb 14, 2022 at 11:46:26AM -0400, Jason Gunthorpe wrote:
> > On Mon, Feb 14, 2022 at 03:18:31PM +0000, Robin Murphy wrote:
> > 
> > > Arguably, iommu_attach_device() could be renamed something like
> > > iommu_attach_group_for_dev(), since that's effectively the semantic that all
> > > the existing API users want anyway (even VFIO at the high level - the group
> > > is the means for the user to assign their GPU/NIC/whatever device to their
> > > process, not the end in itself). That's just a lot more churn.
> > 
> > Right
> 
> Okay, good point. I can live with an iommu_attach_group_for_dev()
> interface, it is still better than making iommu_attach_device() silently
> operate on whole groups.

I think this is what Lu's series currently does, it just doesn't do
the rename churn as Robin noted. Lu, why not add a note like Robin
explained to the kdoc so it is clear this api impacts the whole group?

There is no argument that the internal operation of the iommu layer
should always be using groups - we are just presenting a simplified
API toward drivers.

Jason
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