From: Shameer Kolothum <[email protected]> Add subsections for accel=on (nested Stage-1/Stage-2 translation) and cmdqv (Tegra241 CMDQV hardware command queues) under "User-creatable SMMUv3 devices".
Signed-off-by: Shameer Kolothum <[email protected]> Message-id: [email protected] Reviewed-by: Peter Maydell <[email protected]> Signed-off-by: Peter Maydell <[email protected]> --- docs/system/arm/virt.rst | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst index f811e662d6..ae0be35d57 100644 --- a/docs/system/arm/virt.rst +++ b/docs/system/arm/virt.rst @@ -288,6 +288,32 @@ User-creatable SMMUv3 devices -device pxb-pcie,id=pcie.1,numa_node=1 -device arm-smmuv3,primary-bus=pcie.1,id=smmuv3.1 + *Accelerated SMMUv3 (nested translation)* + + The ``accel=on`` option enables hardware-accelerated nested translation + for vfio-pci passthrough devices. In this mode the guest SMMU driver + programs its own Stage-1 page tables, with the host SMMUv3 handling both + Stage-1 (guest) and Stage-2 (host) translations in hardware. The host + SMMUv3 must support nested translation. This mode requires the iommufd + backend and is only supported when booting with ACPI (not device tree). + + When ``accel=on``, QEMU automatically derives the values for the + ``ril``, ``ats``, ``oas``, ``ssidsize`` and ``cmdqv`` sub-options + from the host SMMUv3 capabilities unless they are set explicitly. + + Example:: + + -device arm-smmuv3,primary-bus=pcie.0,id=smmuv3.0,accel=on + + *Accelerated SMMUv3 command queues (Tegra241 CMDQV)* + + The ``cmdqv`` sub-option enables NVIDIA Tegra241 Command Queue + Virtualization (CMDQV) on supported hosts. With CMDQV, each accelerated + ``arm-smmuv3`` device gets dedicated hardware command queues and the + guest issues SMMU invalidation commands directly to real hardware, + bypassing QEMU and improving throughput for workloads that issue many + invalidations. Without it, every invalidation command traps into QEMU. + Linux guest kernel configuration """""""""""""""""""""""""""""""" -- 2.43.0
