From: Nicolin Chen <nicolinc@nvidia.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
"joro@8bytes.org" <joro@8bytes.org>,
"will@kernel.org" <will@kernel.org>,
"robin.murphy@arm.com" <robin.murphy@arm.com>,
"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
"shuah@kernel.org" <shuah@kernel.org>,
"Liu, Yi L" <yi.l.liu@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>,
"baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>
Subject: Re: [PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain()
Date: Tue, 14 Feb 2023 17:58:36 -0800 [thread overview]
Message-ID: <Y+w8TJ2jfDATftbr@Asurada-Nvidia> (raw)
In-Reply-To: <BN9PR11MB5276CBCF780BD7C61154BF8B8CA39@BN9PR11MB5276.namprd11.prod.outlook.com>
On Wed, Feb 15, 2023 at 01:37:19AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Tuesday, February 14, 2023 6:54 PM
> >
> > On Mon, Feb 13, 2023 at 10:49:34AM -0400, Jason Gunthorpe wrote:
> > > On Sun, Feb 12, 2023 at 11:48:30PM -0800, Nicolin Chen wrote:
> > >
> > > > What about point 1? If dev2 and dev3 are already replaced when
> > > > doing iommu_group_replace_domain() on dev1, their idev objects
> > > > still have the old hwpt/iopt until user space does another two
> > > > IOCTLs on them, right?
> > >
> > > We have a complicated model for multi-device groups...
> > >
> > > The first device in the group to change domains must move all the
> > > devices in the group
> > >
> > > But userspace is still expected to run through and change all the
> > > other devices
> > >
> > > So replace should be a NOP if the group is already linked to the right
> > > domain.
> > >
> > > This patch needs to make sure that incosistency in the view betwen the
> > > iommu_group and the iommufd model doesn't cause a functional
> > > problem.
> >
> > Yea, I was thinking that we'd need to block any access to the
> > idev->hwpt of a pending device's, before the kernel finishes
> > the "NOP" IOCTL from userspace, maybe with a helper:
> > (iommu_get_domain_for_dev(idev->dev) != idev->hwpt->domain)
> >
>
> I didn't see what would be broken w/o such blocking measure.
>
> Can you elaborate?
iommu_group { idev1, idev2 }
(1) Attach all devices to domain1 {
group->domain = domain1;
idev1->hwpt = hwpt1; // domain1
idev2->hwpt = hwpt1; // domain1
}
(2) Attach (replace) idev1 only to domain2 {
group->domain = domain2
idev1->hwpt = hwpt2; // domain2
idev2->hwpt == domain1 // != iommu_get_domain_for_dev()
}
Then if user space isn't aware of these and continues to do
IOMMU_IOAS_MAP for idev2. Though IOVA mappings may be added
onto the domain2 correctly, yet domain2's iopt itree won't
reflect that, until idev2->hwpt is updated too, right?
And the tricky thing is that, though we advocate a device-
centric uAPI, we'd still have to ask user space to align the
devices in the same iommu_group, which is also not present
in QEMU's RFC v3 series.
The traditional detach+attach flow doesn't seem to have this
issue, since there's no re-entry so the work flow is always
that detaching all devices first before attaching to another
domain.
Thanks
Nic
next prev parent reply other threads:[~2023-02-15 1:58 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-07 21:17 [PATCH v2 00/10] Add IO page table replacement support Nicolin Chen
2023-02-07 21:17 ` [PATCH v2 01/10] iommu: Move dev_iommu_ops() to private header Nicolin Chen
2023-02-09 2:49 ` Tian, Kevin
2023-02-07 21:17 ` [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace_domain() API Nicolin Chen
2023-02-09 2:55 ` Tian, Kevin
2023-02-09 13:23 ` Jason Gunthorpe
2023-02-10 1:34 ` Tian, Kevin
2023-02-10 23:51 ` Alex Williamson
2023-02-11 0:44 ` Jason Gunthorpe
2023-02-13 2:24 ` Tian, Kevin
2023-02-13 8:34 ` Baolu Lu
2023-02-13 14:45 ` Jason Gunthorpe
2023-02-14 3:29 ` Tian, Kevin
2023-02-15 6:10 ` Tian, Kevin
2023-02-15 12:52 ` Jason Gunthorpe
2023-02-22 2:11 ` Tian, Kevin
2023-02-24 0:57 ` Jason Gunthorpe
2023-02-24 8:07 ` Tian, Kevin
2023-02-07 21:17 ` [PATCH v2 03/10] iommufd: Create access in vfio_iommufd_emulated_bind() Nicolin Chen
2023-02-09 2:56 ` Tian, Kevin
2023-02-09 16:15 ` Nicolin Chen
2023-02-09 18:58 ` Eric Farman
2023-02-09 19:54 ` Nicolin Chen
2023-02-07 21:17 ` [PATCH v2 04/10] iommufd/selftest: Add IOMMU_TEST_OP_ACCESS_SET_IOAS coverage Nicolin Chen
2023-02-09 2:59 ` Tian, Kevin
2023-02-07 21:17 ` [PATCH v2 05/10] iommufd: Add replace support in iommufd_access_set_ioas() Nicolin Chen
2023-02-09 3:13 ` Tian, Kevin
2023-02-09 20:28 ` Nicolin Chen
2023-02-09 20:49 ` Jason Gunthorpe
2023-02-09 22:18 ` Nicolin Chen
2023-02-07 21:17 ` [PATCH v2 06/10] iommufd/selftest: Add coverage for access->ioas replacement Nicolin Chen
2023-02-07 21:17 ` [PATCH v2 07/10] iommufd/device: Make hwpt_list list_add/del symmetric Nicolin Chen
2023-02-09 3:23 ` Tian, Kevin
2023-02-09 13:24 ` Jason Gunthorpe
2023-02-10 1:46 ` Tian, Kevin
2023-02-10 21:17 ` Jason Gunthorpe
2023-02-13 2:12 ` Tian, Kevin
2023-02-07 21:18 ` [PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain() Nicolin Chen
2023-02-08 8:08 ` Liu, Yi L
2023-02-09 20:55 ` Nicolin Chen
2023-02-08 8:12 ` Liu, Yi L
2023-02-09 20:56 ` Nicolin Chen
2023-02-09 4:00 ` Tian, Kevin
2023-02-09 21:13 ` Nicolin Chen
2023-02-10 0:01 ` Jason Gunthorpe
2023-02-10 20:50 ` Nicolin Chen
2023-02-10 2:11 ` Tian, Kevin
2023-02-11 0:10 ` Nicolin Chen
2023-02-13 2:34 ` Tian, Kevin
2023-02-13 7:48 ` Nicolin Chen
2023-02-13 8:27 ` Tian, Kevin
2023-02-13 14:49 ` Jason Gunthorpe
2023-02-14 10:54 ` Nicolin Chen
2023-02-15 1:37 ` Tian, Kevin
2023-02-15 1:58 ` Nicolin Chen [this message]
2023-02-15 2:15 ` Tian, Kevin
2023-02-15 7:15 ` Nicolin Chen
2023-02-15 7:24 ` Tian, Kevin
2023-02-15 12:51 ` Jason Gunthorpe
2023-02-14 10:59 ` Nicolin Chen
2023-02-15 1:38 ` Tian, Kevin
2023-02-15 7:16 ` Nicolin Chen
2023-02-07 21:18 ` [PATCH v2 09/10] vfio: Support IO page table replacement Nicolin Chen
2023-02-09 4:06 ` Tian, Kevin
2023-02-07 21:18 ` [PATCH v2 10/10] vfio: Do not allow !ops->dma_unmap in vfio_pin/unpin_pages() Nicolin Chen
2023-02-09 4:10 ` Tian, Kevin
2023-02-09 13:26 ` Jason Gunthorpe
2023-02-09 16:19 ` Nicolin Chen
2023-02-09 2:50 ` [PATCH v2 00/10] Add IO page table replacement support Tian, Kevin
2023-02-09 16:13 ` Nicolin Chen
2023-02-10 1:34 ` Tian, Kevin
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