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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Christoph Hellwig <hch@lst.de>, Joerg Roedel <joro@8bytes.org>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Will Deacon <will@kernel.org>,
	Kirti Wankhede <kwankhede@nvidia.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: RE: [PATCH 3/6] vfio: remove the unused mdev iommu hook
Date: Fri, 14 May 2021 13:17:23 +0000	[thread overview]
Message-ID: <MWHPR11MB18863613CEBE3CDEEB86F4FC8C509@MWHPR11MB1886.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20210513120058.GG1096940@ziepe.ca>

> From: Jason Gunthorpe <jgg@ziepe.ca>
> Sent: Thursday, May 13, 2021 8:01 PM
> 
> On Thu, May 13, 2021 at 03:28:52AM +0000, Tian, Kevin wrote:
> 
> > Are you specially concerned about this iommu_device hack which
> > directly connects mdev_device to iommu layer or the entire removed
> > logic including the aux domain concept? For the former we are now
> > following up the referred thread to find a clean way. But for the latter
> > we feel it's still necessary regardless of how iommu interface is redesigned
> > to support device connection from the upper level driver. The reason is
> > that with mdev or subdevice one physical device could be attached to
> > multiple domains now. there could be a primary domain with DOMAIN_
> > DMA type for DMA_API use by parent driver itself, and multiple auxiliary
> > domains with DOMAIN_UNMANAGED types for subdevices assigned to
> > different VMs.
> 
> Why do we need more domains than just the physical domain for the
> parent? How does auxdomain appear in /dev/ioasid?
> 

Another simple reason. Say you have 4 mdevs each from a different 
parent are attached to an ioasid. If only using physical domain of the 
parent + PASID it means there are 4 domains (thus 4 page tables) under 
this IOASID thus every dma map operation must be replicated in all
4 domains which is really unnecessary. Having the domain created
with ioasid and allow a device attaching to multiple domains is much
cleaner for the upper-layer drivers to work with iommu interface.

Thanks
Kevin

  parent reply	other threads:[~2021-05-14 13:17 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10  6:53 more iommu dead code removal Christoph Hellwig
2021-05-10  6:54 ` [PATCH 1/6] iommu: remove the unused dev_has_feat method Christoph Hellwig
2021-05-10  6:54 ` [PATCH 2/6] iommu: remove the unused iommu_aux_get_pasid interface Christoph Hellwig
2021-05-10  6:54 ` [PATCH 3/6] vfio: remove the unused mdev iommu hook Christoph Hellwig
2021-05-10 15:54   ` Jason Gunthorpe
2021-05-13  3:28     ` Tian, Kevin
2021-05-13 12:00       ` Jason Gunthorpe
2021-05-14  6:27         ` Tian, Kevin
2021-05-14  6:54         ` Tian, Kevin
2021-05-14 12:19           ` Jason Gunthorpe
2021-05-14 12:58             ` Tian, Kevin
2021-05-14 13:31               ` Jason Gunthorpe
2021-05-17 12:22                 ` Joerg Roedel
2021-05-17 12:30                   ` Jason Gunthorpe
2021-05-17 12:53                     ` Joerg Roedel
2021-05-17 13:35                       ` Jason Gunthorpe
2021-05-17 15:35                         ` Joerg Roedel
2021-05-19 15:23                           ` Robin Murphy
2021-05-19 18:06                             ` Jason Gunthorpe
2021-05-19 23:12                               ` Tian, Kevin
2021-05-19 23:24                                 ` Jason Gunthorpe
2021-05-20 14:13                                   ` Robin Murphy
2021-05-20 14:34                                     ` Jason Gunthorpe
2021-05-24 18:18                                       ` Robin Murphy
2021-05-25  0:00                                         ` Jason Gunthorpe
2021-06-30  9:08                           ` Tian, Kevin
2021-07-22 13:34                             ` Christoph Hellwig
2021-07-23  5:36                               ` Tian, Kevin
2021-07-23  5:41                                 ` Christoph Hellwig
2021-07-23  5:44                                   ` Tian, Kevin
2021-07-22  6:02                           ` Tian, Kevin
2021-05-14 13:17         ` Tian, Kevin [this message]
2021-05-14 13:39           ` Jason Gunthorpe
2021-05-14 14:28             ` Tian, Kevin
2021-05-14 14:44               ` Jason Gunthorpe
2021-05-10  6:54 ` [PATCH 4/6] iommu: remove iommu_aux_{attach,detach}_device Christoph Hellwig
2021-05-10  6:54 ` [PATCH 5/6] iommu: remove IOMMU_DEV_FEAT_AUX Christoph Hellwig
2021-05-10  6:54 ` [PATCH 6/6] iommu: remove iommu_dev_feature_enabled Christoph Hellwig
2021-05-10 11:54 ` more iommu dead code removal Jason Gunthorpe

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