From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-6383-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 14E13985EC2 for ; Fri, 22 Nov 2019 14:45:10 +0000 (UTC) Date: Fri, 22 Nov 2019 08:00:46 -0500 From: "Michael S. Tsirkin" Message-ID: <20191122075438-mutt-send-email-mst@kernel.org> References: <20191122105000.800410-1-jean-philippe@linaro.org> MIME-Version: 1.0 In-Reply-To: <20191122105000.800410-1-jean-philippe@linaro.org> Subject: [virtio-dev] Re: [RFC 00/13] virtio-iommu on non-devicetree platforms Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline To: Jean-Philippe Brucker 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, jasowang@redhat.com, jacob.jun.pan@intel.com, eric.auger@redhat.com, sebastien.boeuf@intel.com, kevin.tian@intel.com List-ID: On Fri, Nov 22, 2019 at 11:49:47AM +0100, Jean-Philippe Brucker 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. >=20 > 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: >=20 > (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. >=20 > 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 >=20 > 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. >=20 > (2) In addition, there are some concerns about having virtio depend on > ACPI or DT. Some hypervisors (Firecracker, QEMU microvm, kvmtool x86 > [1]) power? > don't currently implement those methods. >=20 > 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: >=20 > - 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. >=20 > - 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. =09A notifier seems easier for users. What are the disadvantages of =09that? >=09So the current prototype doesn't work for firecracker and > microvm, which rely on virtio-mmio. >=20 > - 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. >=20 > - 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. >=20 > 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. >=20 > In this RFC I present both solutions, but I'd rather not keep all of it. > Please see the individual patches for details: >=20 > (1) Patches 1, 3-10 add support for virtio-iommu to the Linux IORT > driver and patches 2, 11 add the VIOT glue. >=20 > (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. >=20 > 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 >=20 >=20 > 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. >=20 > 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 >=20 > 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 =3D> }/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 =3D> }/iort.c (86%) > create mode 100644 drivers/acpi/viot.c > create mode 100644 include/linux/acpi_viot.h >=20 > Jean-Philippe Brucker (1): > iommu/virtio: Add topology description to virtio-iommu config space >=20 > 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 >=20 >=20 > [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/ > --=20 > 2.24.0 --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org