[RFC v1 0/5] Hyper-V: Add para-virtualized IOMMU support for Linux guests

Yu Zhang
2025-12-09T05:11:36Z

This patch series introduces a para-virtualized IOMMU driver for
Linux guests running on Microsoft Hyper-V. The primary objective
is to enable hardware-assisted DMA isolation and scalable device
assignment for Hyper-V child partitions, bypassing the performance
overhead and complexity associated with emulated IOMMU hardware.

The driver implements the following core functionality:
* Hypercall-based Enumeration
Unlike traditional ACPI-based discovery (e.g., DMAR/IVRS),
this driver enumerates the Hyper-V IOMMU capabilities directly
via hypercalls. This approach allows the guest to discover
IOMMU presence and features without requiring specific virtual
firmware extensions or modifications.

* Domain Management
The driver manages IOMMU domains through a new set of Hyper-V
hypercall interfaces, handling domain allocation, attachment,
and detachment for endpoint devices.

* IOTLB Invalidation
IOTLB invalidation requests are marshaled and issued to the
hypervisor through the same hypercall mechanism.

* Nested Translation Support
This implementation leverages guest-managed stage-1 I/O page
tables nested with host stage-2 translations. It is built
upon the consolidated IOMMU page table framework designed by
Jason Gunthorpe [1]. This design eliminates the need for complex
emulation during map operations and ensures scalability across
different architectures.

Implementation Notes:
* Architecture Independence
While the current implementation only supports x86 platforms (Intel
VT-d and AMD IOMMU), the driver design aims to be as architecture-
agnostic as possible. To achieve this, initialization occurs via
`device_initcall` rather than `x86_init.iommu.iommu_init`, and shutdown
is handled via `syscore_ops` instead of `x86_platform.iommu_shutdown`.

* MSI Region Handling
In this RFC, the hardware MSI region is hard-coded to the standard
x86 interrupt range (0xfee00000 - 0xfeefffff). Future updates may
allow this configuration to be queried via hypercalls if new hardware
platforms are to be supported.

* Reserved Regions (RMRR)
There is currently no requirement to support assigned devices with
ACPI RMRR limitations. Consequently, this patch series does not specify
or query reserved memory regions.

Testing:
This series has been validated using dmatest with Intel DSA devices
assigned to the child partition. The tests confirmed successful DMA
transactions under the para-virtualized IOMMU.

Future Work:
* Page-selective IOTLB Invalidation
The current implementation relies on full-domain flushes. Support
for page-selective invalidation is planned for a future series.

* Advanced Features
Support for vSVA and virtual PRI will be addressed in subsequent
updates.

* Root Partition Co-existence
Ensure compatibility with the distinct para-virtualized IOMMU driver
used by Hyper-V's Linux root partition, in which the DMA remapping
is not achieved by stage-1 IO page tables and another set of iommu
ops is provided.

[1] https://github.com/jgunthorpe/linux/tree/iommu_pt_all

Easwar Hariharan (2):
PCI: hv: Create and export hv_build_logical_dev_id()
iommu: Move Hyper-V IOMMU driver to its own subdirectory

Wei Liu (1):
hyperv: Introduce new hypercall interfaces used by Hyper-V guest IOMMU

Yu Zhang (2):
hyperv: allow hypercall output pages to be allocated for child
partitions
iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest

drivers/hv/hv_common.c | 21 +-
drivers/iommu/Kconfig | 10 +-
drivers/iommu/Makefile | 2 +-
drivers/iommu/hyperv/Kconfig | 24 +
drivers/iommu/hyperv/Makefile | 3 +
drivers/iommu/hyperv/iommu.c | 608 ++++++++++++++++++
drivers/iommu/hyperv/iommu.h | 53 ++
.../irq_remapping.c} | 2 +-
drivers/pci/controller/pci-hyperv.c | 28 +-
include/asm-generic/mshyperv.h | 2 +
include/hyperv/hvgdk_mini.h | 8 +
include/hyperv/hvhdk_mini.h | 123 ++++
12 files changed, 850 insertions(+), 34 deletions(-)
create mode 100644 drivers/iommu/hyperv/Kconfig
create mode 100644 drivers/iommu/hyperv/Makefile
create mode 100644 drivers/iommu/hyperv/iommu.c
create mode 100644 drivers/iommu/hyperv/iommu.h
rename drivers/iommu/{hyperv-iommu.c => hyperv/irq_remapping.c} (99%)

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2.49.0