From: "Jacob Pan (Jun)" <jacob.jun.pan@intel.com>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: <linux-acpi@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<iommu@lists.linux-foundation.org>,
<virtualization@lists.linux-foundation.org>,
<linux-pci@vger.kernel.org>, <virtio-dev@lists.oasis-open.org>,
<rjw@rjwysocki.net>, <lenb@kernel.org>,
<lorenzo.pieralisi@arm.com>, <guohanjun@huawei.com>,
<sudeep.holla@arm.com>, <gregkh@linuxfoundation.org>,
<joro@8bytes.org>, <bhelgaas@google.com>, <mst@redhat.com>,
<jasowang@redhat.com>, <eric.auger@redhat.com>,
<sebastien.boeuf@intel.com>, <kevin.tian@intel.com>,
jacob.jun.pan@intel.com
Subject: Re: [RFC 00/13] virtio-iommu on non-devicetree platforms
Date: Fri, 22 Nov 2019 16:01:02 -0800 [thread overview]
Message-ID: <20191122160102.00004489@intel.com> (raw)
In-Reply-To: <20191122105000.800410-1-jean-philippe@linaro.org>
On Fri, 22 Nov 2019 11:49:47 +0100
Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:
> I'm seeking feedback on multi-platform support for virtio-iommu. At
> the moment only devicetree (DT) is supported and we don't have a
> pleasant solution for other platforms. Once we figure out the topology
> description, x86 support is trivial.
>
> Since the IOMMU manages memory accesses from other devices, the guest
> kernel needs to initialize the IOMMU before endpoints start issuing
> DMA. It's a solved problem: firmware or hypervisor describes through
> DT or ACPI tables the device dependencies, and probe of endpoints is
> deferred until the IOMMU is probed. But:
>
> (1) ACPI has one table per vendor (DMAR for Intel, IVRS for AMD and
> IORT for Arm). From my point of view IORT is easier to extend, since
> we just need to introduce a new node type. There are no dependencies
> to Arm in the Linux IORT driver, so it works well with CONFIG_X86.
>
From my limited understanding, IORT and VIOT is to solve device topology
enumeration only? I am not sure how it can be expanded to cover
information beyond device topology. e.g. DMAR has NUMA information and
root port ATS, I guess they are not used today in the guest but might
be additions in the future.
> However, there are concerns about other OS vendors feeling
> obligated to implement this new node, so Arm proposed introducing
> another ACPI table, that can wrap any of DMAR, IVRS and IORT to
> extend it with new virtual nodes. A draft of this VIOT table
> specification is available at
> http://jpbrucker.net/virtio-iommu/viot/viot-v5.pdf
>
> I'm afraid this could increase fragmentation as guests would need
> to implement or modify their support for all of DMAR, IVRS and IORT.
> If we end up doing VIOT, I suggest limiting it to IORT.
>
> (2) In addition, there are some concerns about having virtio depend on
> ACPI or DT. Some hypervisors (Firecracker, QEMU microvm, kvmtool
> x86 [1]) don't currently implement those methods.
>
> It was suggested to embed the topology description into the
> device. It can work, as demonstrated at the end of this RFC, with the
> following limitations:
>
> - The topology description must be read before any endpoint
> managed by the IOMMU is probed, and even before the virtio module is
> loaded. This RFC uses a PCI quirk to manually parse the virtio
> configuration. It assumes that all endpoints managed by the
> IOMMU are under this same PCI host.
>
> - I don't have a solution for the virtio-mmio transport at the
> moment, because I haven't had time to modify a host to test it.
> I think it could either use a notifier on the platform bus, or
> better, a new 'iommu' command-line argument to the virtio-mmio
> driver. So the current prototype doesn't work for firecracker
> and microvm, which rely on virtio-mmio.
>
> - For Arm, if the platform has an ITS, the hypervisor needs IORT
> or DT to describe it anyway. More generally, not using either ACPI or
> DT might prevent from supporting other features as well. I
> suspect the above users will have to implement a standard method
> sooner or later.
>
> - Even when reusing as much existing code as possible, guest
> support is still going to be around a few hundred lines since we can't
> rely on the normal virtio infrastructure to be loaded at that
> point. As you can see below, the diffstat for the incomplete
> topology implementation is already bigger than the exhaustive
> IORT support, even when jumping through the VIOT hoop.
>
> So it's a lightweight solution for very specific use-cases, and we
> should still support ACPI for the general case. Multi-platform
> guests such as Linux will then need to support three topology
> descriptions instead of two.
>
> In this RFC I present both solutions, but I'd rather not keep all of
> it. Please see the individual patches for details:
>
> (1) Patches 1, 3-10 add support for virtio-iommu to the Linux IORT
> driver and patches 2, 11 add the VIOT glue.
>
> (2) Patch 12 adds the built-in topology description to the
> virtio-iommu specification. Patch 13 is a partial implementation for
> the Linux virtio-iommu driver. It only supports PCI, not platform
> devices.
>
> You can find Linux and QEMU code on my virtio-iommu/devel branches at
> http://jpbrucker.net/git/linux and http://jpbrucker.net/git/qemu
>
>
> I split the diffstat since there are two independent features. The
> first one is for patches 1-11, and the second one for patch 13.
>
> Jean-Philippe Brucker (11):
> ACPI/IORT: Move IORT to the ACPI folder
> ACPI: Add VIOT definitions
> ACPI/IORT: Allow registration of external tables
> ACPI/IORT: Add node categories
> ACPI/IORT: Support VIOT virtio-mmio node
> ACPI/IORT: Support VIOT virtio-pci node
> ACPI/IORT: Defer probe until virtio-iommu-pci has registered a
> fwnode ACPI/IORT: Add callback to update a device's fwnode
> iommu/virtio: Create fwnode if necessary
> iommu/virtio: Update IORT fwnode
> ACPI: Add VIOT table
>
> MAINTAINERS | 9 +
> drivers/acpi/Kconfig | 7 +
> drivers/acpi/Makefile | 2 +
> drivers/acpi/arm64/Kconfig | 3 -
> drivers/acpi/arm64/Makefile | 1 -
> drivers/acpi/bus.c | 2 +
> drivers/acpi/{arm64 => }/iort.c | 317
> ++++++++++++++++++++++++++------ drivers/acpi/tables.c |
> 2 +- drivers/acpi/viot.c | 44 +++++
> drivers/iommu/Kconfig | 1 +
> drivers/iommu/virtio-iommu.c | 61 +++++-
> include/acpi/actbl2.h | 31 ++++
> include/linux/acpi_iort.h | 14 ++
> include/linux/acpi_viot.h | 20 ++
> 14 files changed, 448 insertions(+), 66 deletions(-)
> rename drivers/acpi/{arm64 => }/iort.c (86%)
> create mode 100644 drivers/acpi/viot.c
> create mode 100644 include/linux/acpi_viot.h
>
> Jean-Philippe Brucker (1):
> iommu/virtio: Add topology description to virtio-iommu config space
>
> drivers/base/platform.c | 3 +
> drivers/iommu/Kconfig | 9 +
> drivers/iommu/Makefile | 1 +
> drivers/iommu/virtio-iommu-topology.c | 410
> ++++++++++++++++++++++++++ drivers/iommu/virtio-iommu.c |
> 3 + drivers/pci/pci-driver.c | 3 +
> include/linux/virtio_iommu.h | 18 ++
> include/uapi/linux/virtio_iommu.h | 26 ++
> 8 files changed, 473 insertions(+)
> create mode 100644 drivers/iommu/virtio-iommu-topology.c
> create mode 100644 include/linux/virtio_iommu.h
>
>
> [1] firecracker: https://github.com/firecracker-microvm/firecracker
> microvm: https://github.com/qemu/qemu/blob/master/docs/microvm.rst
> kvmtool:
> https://git.kernel.org/pub/scm/linux/kernel/git/will/kvmtool.git/
next prev parent reply other threads:[~2019-11-23 0:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-22 10:49 [RFC 00/13] virtio-iommu on non-devicetree platforms Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 01/13] ACPI/IORT: Move IORT to the ACPI folder Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 02/13] ACPI: Add VIOT definitions Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 03/13] ACPI/IORT: Allow registration of external tables Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 04/13] ACPI/IORT: Add node categories Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 05/13] ACPI/IORT: Support VIOT virtio-mmio node Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 06/13] ACPI/IORT: Support VIOT virtio-pci node Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 07/13] ACPI/IORT: Defer probe until virtio-iommu-pci has registered a fwnode Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 08/13] ACPI/IORT: Add callback to update a device's fwnode Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 09/13] iommu/virtio: Create fwnode if necessary Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 10/13] iommu/virtio: Update IORT fwnode Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC 11/13] ACPI: Add VIOT table Jean-Philippe Brucker
2019-11-22 10:49 ` [RFC virtio 12/13] virtio-iommu: Add built-in topology description Jean-Philippe Brucker
2019-11-22 10:50 ` [RFC 13/13] iommu/virtio: Add topology description to Jean-Philippe Brucker
2019-11-22 12:53 ` Michael S. Tsirkin
2019-11-25 17:48 ` Jean-Philippe Brucker
2019-11-22 13:00 ` [RFC 00/13] virtio-iommu on non-devicetree platforms Michael S. Tsirkin
2019-11-25 17:53 ` Jean-Philippe Brucker
2019-11-23 0:01 ` Jacob Pan (Jun) [this message]
2019-11-25 18:02 ` Jean-Philippe Brucker
2019-12-04 3:01 ` Jacob Pan (Jun)
2019-12-18 11:20 ` Jean-Philippe Brucker
2019-12-20 18:54 ` Jacob Pan (Jun)
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