From 3c445dacc47f43d2e66280d393b71ac8e5bb01bb Mon Sep 17 00:00:00 2001 From: Daniel Henrique Barboza Date: Wed, 16 Oct 2024 17:40:28 -0300 Subject: pci-ids.rst: add Red Hat pci-id for RISC-V IOMMU device The RISC-V IOMMU PCI device we're going to add next is a reference implementation of the riscv-iommu spec [1], which predicts that the IOMMU can be implemented as a PCIe device. However, RISC-V International (RVI), the entity that ratified the riscv-iommu spec, didn't bother assigning a PCI ID for this IOMMU PCIe implementation that the spec predicts. This puts us in an uncommon situation because we want to add the reference IOMMU PCIe implementation but we don't have a PCI ID for it. Given that RVI doesn't provide a PCI ID for it we reached out to Red Hat and Gerd Hoffman, and they were kind enough to give us a PCI ID for the RISC-V IOMMU PCI reference device. Thanks Red Hat and Gerd for this RISC-V IOMMU PCIe device ID. [1] https://github.com/riscv-non-isa/riscv-iommu/releases/tag/v1.0.0 Cc: Gerd Hoffmann Signed-off-by: Daniel Henrique Barboza Reviewed-by: Frank Chang Reviewed-by: Gerd Hoffmann Message-ID: <20241016204038.649340-5-dbarboza@ventanamicro.com> Signed-off-by: Alistair Francis --- docs/specs/pci-ids.rst | 2 ++ 1 file changed, 2 insertions(+) (limited to 'docs/specs') diff --git a/docs/specs/pci-ids.rst b/docs/specs/pci-ids.rst index 328ab31..261b0f3 100644 --- a/docs/specs/pci-ids.rst +++ b/docs/specs/pci-ids.rst @@ -98,6 +98,8 @@ PCI devices (other than virtio): PCI ACPI ERST device (``-device acpi-erst``) 1b36:0013 PCI UFS device (``-device ufs``) +1b36:0014 + PCI RISC-V IOMMU device All these devices are documented in :doc:`index`. -- cgit v1.1 From 77cfbf5d08f8fbcc721b6309c560e4f48bdda8fd Mon Sep 17 00:00:00 2001 From: Daniel Henrique Barboza Date: Wed, 16 Oct 2024 17:40:36 -0300 Subject: docs/specs: add riscv-iommu Add a simple guideline to use the existing RISC-V IOMMU support we just added. This doc will be updated once we add the riscv-iommu-sys device. Signed-off-by: Daniel Henrique Barboza Reviewed-by: Alistair Francis Message-ID: <20241016204038.649340-13-dbarboza@ventanamicro.com> Signed-off-by: Alistair Francis --- docs/specs/index.rst | 1 + docs/specs/riscv-iommu.rst | 90 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 91 insertions(+) create mode 100644 docs/specs/riscv-iommu.rst (limited to 'docs/specs') diff --git a/docs/specs/index.rst b/docs/specs/index.rst index 6495ed5..ff5a1f0 100644 --- a/docs/specs/index.rst +++ b/docs/specs/index.rst @@ -36,3 +36,4 @@ guest hardware that is specific to QEMU. vmgenid rapl-msr rocker + riscv-iommu diff --git a/docs/specs/riscv-iommu.rst b/docs/specs/riscv-iommu.rst new file mode 100644 index 0000000..463f4cf --- /dev/null +++ b/docs/specs/riscv-iommu.rst @@ -0,0 +1,90 @@ +.. _riscv-iommu: + +RISC-V IOMMU support for RISC-V machines +======================================== + +QEMU implements a RISC-V IOMMU emulation based on the RISC-V IOMMU spec +version 1.0 `iommu1.0`_. + +The emulation includes a PCI reference device, riscv-iommu-pci, that QEMU +RISC-V boards can use. The 'virt' RISC-V machine is compatible with this +device. + +riscv-iommu-pci reference device +-------------------------------- + +This device implements the RISC-V IOMMU emulation as recommended by the section +"Integrating an IOMMU as a PCIe device" of `iommu1.0`_: a PCI device with base +class 08h, sub-class 06h and programming interface 00h. + +As a reference device it doesn't implement anything outside of the specification, +so it uses a generic default PCI ID given by QEMU: 1b36:0014. + +To include the device in the 'virt' machine: + +.. code-block:: bash + + $ qemu-system-riscv64 -M virt -device riscv-iommu-pci,[optional_pci_opts] (...) + +This will add a RISC-V IOMMU PCI device in the board following any additional +PCI parameters (like PCI bus address). The behavior of the RISC-V IOMMU is +defined by the spec but its operation is OS dependent. + +As of this writing the existing Linux kernel support `linux-v8`_, not yet merged, +does not have support for features like VFIO passthrough. The IOMMU emulation +was tested using a public Ventana Micro Systems kernel repository in +`ventana-linux`_. This kernel is based on `linux-v8`_ with additional patches that +enable features like KVM VFIO passthrough with irqbypass. Until the kernel support +is feature complete feel free to use the kernel available in the Ventana Micro Systems +mirror. + +The current Linux kernel support will use the IOMMU device to create IOMMU groups +with any eligible cards available in the system, regardless of factors such as the +order in which the devices are added in the command line. + +This means that these command lines are equivalent as far as the current +IOMMU kernel driver behaves: + +.. code-block:: bash + + $ qemu-system-riscv64 \ + -M virt,aia=aplic-imsic,aia-guests=5 \ + -device riscv-iommu-pci,addr=1.0,vendor-id=0x1efd,device-id=0xedf1 \ + -device e1000e,netdev=net1 -netdev user,id=net1,net=192.168.0.0/24 \ + -device e1000e,netdev=net2 -netdev user,id=net2,net=192.168.200.0/24 \ + (...) + + $ qemu-system-riscv64 \ + -M virt,aia=aplic-imsic,aia-guests=5 \ + -device e1000e,netdev=net1 -netdev user,id=net1,net=192.168.0.0/24 \ + -device e1000e,netdev=net2 -netdev user,id=net2,net=192.168.200.0/24 \ + -device riscv-iommu-pci,addr=1.0,vendor-id=0x1efd,device-id=0xedf1 \ + (...) + +Both will create iommu groups for the two e1000e cards. + +Another thing to notice on `linux-v8`_ and `ventana-linux`_ is that the kernel driver +considers an IOMMU identified as a Rivos device, i.e. it uses Rivos vendor ID. To +use the riscv-iommu-pci device with the existing kernel support we need to emulate +a Rivos PCI IOMMU by setting 'vendor-id' and 'device-id': + +.. code-block:: bash + + $ qemu-system-riscv64 -M virt \ + -device riscv-iommu-pci,vendor-id=0x1efd,device-id=0xedf1 (...) + +Several options are available to control the capabilities of the device, namely: + +- "bus": the bus that the IOMMU device uses +- "ioatc-limit": size of the Address Translation Cache (default to 2Mb) +- "intremap": enable/disable MSI support +- "ats": enable ATS support +- "off" (Out-of-reset translation mode: 'on' for DMA disabled, 'off' for 'BARE' (passthrough)) +- "s-stage": enable s-stage support +- "g-stage": enable g-stage support + +.. _iommu1.0: https://github.com/riscv-non-isa/riscv-iommu/releases/download/v1.0/riscv-iommu.pdf + +.. _linux-v8: https://lore.kernel.org/linux-riscv/cover.1718388908.git.tjeznach@rivosinc.com/ + +.. _ventana-linux: https://github.com/ventanamicro/linux/tree/dev-upstream -- cgit v1.1