Re: [PATCH v3 4/5] iommu/hyperv: Add para-virtualized IOMMU support for Hyper-V guest

[Easwar Hariharan <easwar.hariharan@linux.microsoft.com>]

On 8/11/2026 08:50, Yu Zhang wrote:
> Add a para-virtualized IOMMU driver for Linux guests running on Hyper-V.
> This driver implements stage-1 IO translation within the guest OS.
> It integrates with the Linux IOMMU core, utilizing Hyper-V hypercalls
> for:
>  - Capability discovery
>  - Domain allocation, configuration, and deallocation
>  - Device attachment and detachment
>  - IOTLB invalidation
> 
> The driver constructs x86-compatible stage-1 IO page tables in the
> guest memory using consolidated IO page table helpers. This allows
> the guest to manage stage-1 translations independently of vendor-
> specific drivers (like Intel VT-d or AMD IOMMU).
> 
> Hyper-V consumes this stage-1 IO page table when a device domain is
> created and configured, and nests it with the host's stage-2 IO page
> tables, therefore eliminating the VM exits for guest IOMMU mapping
> operations. For unmapping operations, VM exits to perform the IOTLB
> flush are still unavoidable.
> 
> Guest hibernation and resume are not supported by this initial
> implementation. The guest-owned stage-1 page tables reside in guest
> memory and are preserved in the hibernation image. However, the image
> does not by itself preserve the Hyper-V device-domain objects or their
> device attachments, and the current pvIOMMU interface does not define
> whether or how Hyper-V restores that state.
> 
> To identify a device in its hypercall interface, the driver looks up the
> logical device ID prefix registered for the device's PCI domain (see the
> logical device ID registry in hv_common.c) and combines it with the PCI
> function number of the endpoint device.
> 
> Co-developed-by: Wei Liu <wei.liu@kernel.org>
> Signed-off-by: Wei Liu <wei.liu@kernel.org>
> Co-developed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
> Signed-off-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
> Signed-off-by: Yu Zhang <zhangyu1@linux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_init.c             |   4 +
>  arch/x86/include/asm/mshyperv.h       |   4 +
>  drivers/iommu/Kconfig                 |   1 +
>  drivers/iommu/hyperv/Kconfig          |  16 +
>  drivers/iommu/hyperv/Makefile         |   1 +
>  drivers/iommu/hyperv/hv-iommu-guest.c | 632 ++++++++++++++++++++++++++
>  drivers/iommu/hyperv/iommu.h          |  50 ++
>  7 files changed, 708 insertions(+)
>  create mode 100644 drivers/iommu/hyperv/Kconfig
>  create mode 100644 drivers/iommu/hyperv/hv-iommu-guest.c
>  create mode 100644 drivers/iommu/hyperv/iommu.h
> 
Seems like this is missing a change to MAINTAINERS. I'd suggest making a new section
and adding both the IOMMU and Hyper-V lists. As it stands, the IOMMU list will get no
notification of changes to this driver.

Thanks,
Easwar (he/him)