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
next prev 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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