Re: [PATCH v0 00/15] PCI passthru on Hyper-V (Part I)

Jacob Pan
2026-01-20T21:50:35Z

Hi Mukesh,

On Mon, 19 Jan 2026 22:42:15 -0800
Mukesh R <mrathor@linux.microsoft.com> wrote:

> From: Mukesh Rathor <mrathor@linux.microsoft.com>
>
> Implement passthru of PCI devices to unprivileged virtual machines
> (VMs) when Linux is running as a privileged VM on Microsoft Hyper-V
> hypervisor. This support is made to fit within the workings of VFIO
> framework, and any VMM needing to use it must use the VFIO subsystem.
> This supports both full device passthru and SR-IOV based VFs.
>
> There are 3 cases where Linux can run as a privileged VM (aka MSHV):
> Baremetal root (meaning Hyper-V+Linux), L1VH, and Nested.
>
I think some introduction/background to L1VH would help.

> At a high level, the hypervisor supports traditional mapped iommu
> domains that use explicit map and unmap hypercalls for mapping and
> unmapping guest RAM into the iommu subsystem.
It may be clearer to state that the hypervisor supports Linux IOMMU
paging domains through map/unmap hypercalls, mapping GPAs to HPAs using
stage‑2 I/O page tables.

> Hyper-V also has a
> concept of direct attach devices whereby the iommu subsystem simply
> uses the guest HW page table (ept/npt/..). This series adds support
> for both, and both are made to work in VFIO type1 subsystem.
>
This may warrant introducing a new IOMMU domain feature flag, as it
performs mappings but does not support map/unmap semantics in the same
way as a paging domain.

> While this Part I focuses on memory mappings, upcoming Part II
> will focus on irq bypass along with some minor irq remapping
> updates.
>
> This patch series was tested using Cloud Hypervisor verion 48. Qemu
> support of MSHV is in the works, and that will be extended to include
> PCI passthru and SR-IOV support also in near future.
>
> Based on: 8f0b4cce4481 (origin/hyperv-next)
>
> Thanks,
> -Mukesh
>
> Mukesh Rathor (15):
> iommu/hyperv: rename hyperv-iommu.c to hyperv-irq.c
> x86/hyperv: cosmetic changes in irqdomain.c for readability
> x86/hyperv: add insufficient memory support in irqdomain.c
> mshv: Provide a way to get partition id if running in a VMM process
> mshv: Declarations and definitions for VFIO-MSHV bridge device
> mshv: Implement mshv bridge device for VFIO
> mshv: Add ioctl support for MSHV-VFIO bridge device
> PCI: hv: rename hv_compose_msi_msg to hv_vmbus_compose_msi_msg
> mshv: Import data structs around device domains and irq remapping
> PCI: hv: Build device id for a VMBus device
> x86/hyperv: Build logical device ids for PCI passthru hcalls
> x86/hyperv: Implement hyperv virtual iommu
> x86/hyperv: Basic interrupt support for direct attached devices
> mshv: Remove mapping of mmio space during map user ioctl
> mshv: Populate mmio mappings for PCI passthru
>
> MAINTAINERS | 1 +
> arch/arm64/include/asm/mshyperv.h | 15 +
> arch/x86/hyperv/irqdomain.c | 314 ++++++---
> arch/x86/include/asm/mshyperv.h | 21 +
> arch/x86/kernel/pci-dma.c | 2 +
> drivers/hv/Makefile | 3 +-
> drivers/hv/mshv_root.h | 24 +
> drivers/hv/mshv_root_main.c | 296 +++++++-
> drivers/hv/mshv_vfio.c | 210 ++++++
> drivers/iommu/Kconfig | 1 +
> drivers/iommu/Makefile | 2 +-
> drivers/iommu/hyperv-iommu.c | 1004
> +++++++++++++++++++++------ drivers/iommu/hyperv-irq.c |
> 330 +++++++++ drivers/pci/controller/pci-hyperv.c | 207 ++++--
> include/asm-generic/mshyperv.h | 1 +
> include/hyperv/hvgdk_mini.h | 11 +
> include/hyperv/hvhdk_mini.h | 112 +++
> include/linux/hyperv.h | 6 +
> include/uapi/linux/mshv.h | 31 +
> 19 files changed, 2182 insertions(+), 409 deletions(-)
> create mode 100644 drivers/hv/mshv_vfio.c
> create mode 100644 drivers/iommu/hyperv-irq.c
>