From: Jason Gunthorpe <jgg@nvidia.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: kvm@vger.kernel.org, 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>,
Stuart Yoder <stuyoder@gmail.com>,
Kevin Tian <kevin.tian@intel.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Alex Williamson <alex.williamson@redhat.com>,
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>
Subject: Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()
Date: Mon, 14 Feb 2022 13:25:52 -0400 [thread overview]
Message-ID: <20220214172552.GG4160@nvidia.com> (raw)
In-Reply-To: <f302e823-ecc3-2aae-e275-85a56e26fb25@arm.com>
On Mon, Feb 14, 2022 at 04:38:23PM +0000, Robin Murphy wrote:
> > This works better because the iommu code can hold the internal group
> > while it finds the bus/device and then invokes the driver op. We don't
> > have a lifetime problem anymore under that lock.
>
> That's certainly one of the cleaner possibilities - per the theme of this
> thread I'm not hugely keen on proliferating special VFIO-specific
> versions
IMHO this is still a net better than VFIO open coding buggy versions
as it has done.
> of IOMMU APIs, but trying to take the dev->mutex might be a bit heavy-handed
> and risky,
The container->group lock is held during this code, and the
container->group_lock is taken during probe under the
dev_mutex. Acquiring the dev_mutex inside the group_lock should not be
done.
> and getting at the vfio_group->device_lock a bit fiddly, so if I
> can't come up with anything nicer or more general it might be a fair
> compromise.
Actually that doesn't look so bad. A 'vfio allocate domain from group'
function that used the above trick looks OK to me right now.
If we could move the iommu_capable() test to a domain that would make
this pretty nice - getting the bus safely is a bit more of a PITA -
I'm much less keen on holding the device_lock for the whole function.
> > The remaining VFIO use of bus for iommu_capable() is better done
> > against the domain or the group object, as appropriate.
>
> Indeed, although half the implementations of .capable are nonsense already,
> so I'm treating that one as a secondary priority for the moment (with an aim
> to come back afterwards and just try to kill it off as far as possible).
> RDMA and VFIO shouldn't be a serious concern for the kind of systems with
> heterogeneous IOMMUs at this point.
Well, lets see:
drivers/infiniband/hw/usnic/usnic_uiom.c: if (!iommu_capable(dev->bus, IOMMU_CAP_CACHE_COHERENCY)) {
drivers/vhost/vdpa.c: if (!iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
These are kind of hacky ways to say "userspace can actually do DMA
because we don't need privileged cache flush instructions on this
platform". I would love it if these could be moved to some struct
device API - I've aruged with Christoph a couple of times we need
something like that..
drivers/vfio/vfio_iommu_type1.c: if (iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
This is doing the above, and also the no-snoop mess that Intel has
mixed in. How to exactly properly expose their special no-snoop
behavior is definitely something that should be on the domain.
drivers/pci/controller/vmd.c: if (iommu_capable(vmd->dev->dev.bus, IOMMU_CAP_INTR_REMAP) ||
drivers/vfio/vfio_iommu_type1.c: iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
Not sure about VMD, but the VFIO one is a security statement. It could
be quite happy as a domain query, or a flag 'require secure MSI
interrupts' as input to attach_domain.
> > > solving it on my own and end up deleting
> > > iommu_group_replace_domain() in about 6 months' time anyway.
> >
> > I expect this API to remain until we figure out a solution to the PPC
> > problem, and come up with an alternative way to change the attached
> > domain on the fly.
>
> I though PPC wasn't using the IOMMU API at all... or is that the problem?
It needs it both ways, a way to get all the DMA security properties
from Lu's series without currently using an iommu_domain to get
them. So the design is to attach a NULL domain for PPC and leave it
like that.
It is surely eventually fixable to introduce a domain to PPC, I would
just prefer we not make anything contingent on actually doing that. :\
Jason
next prev parent reply other threads:[~2022-02-14 17:26 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-06 2:20 [PATCH v1 0/8] Scrap iommu_attach/detach_group() interfaces Lu Baolu
2022-01-06 2:20 ` [PATCH v1 1/8] iommu: Add iommu_group_replace_domain() Lu Baolu
2022-01-06 17:06 ` Jason Gunthorpe
2022-01-07 0:26 ` Lu Baolu
2022-02-14 12:09 ` Robin Murphy
2022-02-14 12:45 ` Jason Gunthorpe
2022-02-14 14:10 ` Robin Murphy
2022-02-14 14:56 ` Jason Gunthorpe
2022-02-14 16:38 ` Robin Murphy
2022-02-14 17:25 ` Jason Gunthorpe [this message]
2022-01-06 2:20 ` [PATCH v1 2/8] vfio/type1: Use iommu_group_replace_domain() Lu Baolu
2022-01-06 2:20 ` [PATCH v1 3/8] iommu: Extend iommu_at[de]tach_device() for multi-device groups Lu Baolu
2022-01-06 17:22 ` Jason Gunthorpe
2022-01-07 1:14 ` Lu Baolu
2022-01-07 1:19 ` Jason Gunthorpe
2022-02-14 11:39 ` Joerg Roedel
2022-02-14 13:03 ` Jason Gunthorpe
2022-02-14 14:39 ` Joerg Roedel
2022-02-14 15:18 ` Robin Murphy
2022-02-14 15:46 ` Jason Gunthorpe
2022-02-15 8:58 ` Joerg Roedel
2022-02-15 13:47 ` Jason Gunthorpe
2022-02-16 6:28 ` Lu Baolu
2022-02-16 13:54 ` Jason Gunthorpe
2022-01-06 2:20 ` [PATCH v1 4/8] drm/tegra: Use iommu_attach/detatch_device() Lu Baolu
2022-01-06 2:20 ` [PATCH v1 5/8] iommu/amd: Use iommu_attach/detach_device() Lu Baolu
2022-01-06 14:33 ` Jason Gunthorpe
2022-01-07 0:23 ` Lu Baolu
2022-02-14 11:27 ` Joerg Roedel
2022-02-14 13:15 ` Jason Gunthorpe
2022-02-14 13:40 ` Joerg Roedel
2022-02-14 14:02 ` Jason Gunthorpe
2022-02-14 14:23 ` Joerg Roedel
2022-02-14 15:00 ` Jason Gunthorpe
2022-02-15 9:11 ` Joerg Roedel
2022-02-15 13:02 ` Robin Murphy
2022-02-15 14:37 ` Jason Gunthorpe
2022-01-06 2:20 ` [PATCH v1 6/8] gpu/host1x: " Lu Baolu
2022-01-06 15:35 ` Jason Gunthorpe
2022-01-07 0:35 ` Lu Baolu
2022-01-07 0:48 ` Jason Gunthorpe
2022-01-07 1:19 ` Lu Baolu
2022-01-06 2:20 ` [PATCH v1 7/8] media: staging: media: tegra-vde: " Lu Baolu
2022-01-06 2:20 ` [PATCH v1 8/8] iommu: Remove iommu_attach/detach_group() Lu Baolu
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