[hyperv-next,v5,00/11] arm64: hyperv: Support Virtual Trust Level Boot

This patch set allows the Hyper-V code to boot on ARM64 inside a Virtual Trust
Level. These levels are a part of the Virtual Secure Mode documented in the
Top-Level Functional Specification available at
https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/vsm.

The OpenHCL paravisor https://github.com/microsoft/openvmm/tree/main/openhcl
can serve as a practical application of these patches on ARM64.

For validation, I built kernels for the {x86_64, ARM64} x {VTL0, VTL2} set with
a small initrd embedded into the kernel and booted VMs managed by Hyper-V and
OpenVMM off of that.

Starting from V5, the patch series includes a non-functional change to KVM on
arm64 which I tested as well.

[V5]
    - Provide and use a common SMCCC-based infra for the arm64 hypervisor guests
      to detect hypervisor presence.
    ** Thank you, Arnd! **

    - Fix line wraps to follow the rest of the code.
    - Open-code getting IRQ domain parent in the ACPI case to make the code
      better.
    ** Thank you, Bjorn! **

    - Test the binding with the latest dtschema.
    - Clean up the commit title and description.
    - Use proper defines for known constants.
    ** Thank you, Krzysztof! **

    - Extend comment on why ACPI v6 is checked for.
    - Reorder patches to make sure that even with partial series application
      the compilation succeeds.
    - Report VTL the kernel runs in.
    - Use "X86_64" in Kconfig rather than "X86".
    - Extract a non-functional change for hv_get_vmbus_root_device() into
      a separate patch.
    ** Thank you, Michael! **

[V4]
    https://lore.kernel.org/linux-hyperv/20250212014321.1108840-1-romank@linux.microsoft.com/
    - Fixed wording to match acronyms defined in the "Terms and Abbreviations"
      section of the SMCCC specification throughout the patch series.
      **Thank you, Michael!**

    - Replaced the hypervisor ID containing ASCII with an UUID as
      required by the specification.
      **Thank you, Michael!**

    - Added an explicit check for `SMCCC_RET_NOT_SUPPORTED` when discovering the
      hypervisor presence to make the backward compatibility obvious.
      **Thank you, Saurabh!**

    - Split the fix for `get_vtl(void)` out to make it easier to backport.
    - Refactored the configuration options as requested to eliminate the risk
      of building non-functional kernels with randomly selected options.
      **Thank you, Michael!**

    - Refactored the changes not to introduce an additional file with
      a one-line function.
      **Thank you, Wei!**

    - Fixed change description for the VMBus DeviceTree changes, used
      `scripts/get_maintainers.pl` on the latest kernel to get the up-to-date list
      of maintainers as requested.
      **Thank you, Krzysztof!**

    - Removed the added (paranoidal+superfluous) checks for DMA coherence in the
      VMBus driver and instead relied on the DMA and the OF subsystem code.
      **Thank you, Arnd, Krzysztof, Michael!**

    - Used another set of APIs for discovering the hardware interrupt number
      in the VMBus driver to be able to build the driver as a module.
      **Thank you, Michael, Saurabh!**

    - Renamed the newly introduced `get_vmbus_root_device(void)` function to
      `hv_get_vmbus_root_device(void)` as requested.
      **Thank you, Wei!**

    - Applied the suggested small-scale refactoring to simplify changes to the Hyper-V
      PCI driver. Taking the offered liberty of doing the large scale refactoring
      in another patch series.
      **Thank you, Michael!**

    - Added a fix for the issue discovered internally where the CPU would not
      get the interrupt from a PCI device attached to VTL2 as the shared peripheral
      interrupt number (SPI) was not offset by 32 (the first valid SPI number).
      **Thank you, Brian!**

[V3]
    https://lore.kernel.org/lkml/20240726225910.1912537-1-romank@linux.microsoft.com/
    - Employed the SMCCC function recently implemented in the Microsoft Hyper-V
      hypervisor to detect running on Hyper-V/arm64. No dependence on ACPI/DT is
      needed anymore although the source code still falls back to ACPI as the new
      hypervisor might be available only in the Windows Insiders channel just
      yet.
    - As a part of the above, refactored detecting the hypervisor via ACPI FADT.
    - There was a suggestion to explore whether it is feasible or not to express
      that ACPI must be absent for the VTL mode and present for the regular guests
      in the Hyper-V Kconfig file.
      My current conclusion is that this will require refactoring in many places.
      That becomes especially convoluted on x86_64 due to the MSI and APIC
      dependencies. I'd ask to let us tackle that in another patch series (or chalk
      up to nice-have's rather than fires to put out) to separate concerns and
      decrease chances of breakage.
    - While refactoring `get_vtl(void)` and the related code, fixed the hypercall
      output address not to overlap with the input as the Hyper-V TLFS mandates:
      "The input and output parameter lists cannot overlap or cross page boundaries."
      See https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface
      for more.
      Some might argue that should've been a topic for a separate patch series;
      I'd counter that the change is well-contained (one line), has no dependencies,
      and makes the code legal.
    - Made the VTL boot code (c)leaner as was suggested.
    - Set DMA cache coherency for the VMBus.
    - Updated DT bindings in the VMBus documentation (separated out into a new patch).
    - Fixed `vmbus_set_irq` to use the API that works both for the ACPI and OF.
    - Reworked setting up the vPCI MSI IRQ domain in the non-ACPI case. The logic
      looks a bit fiddly/ad-hoc as I couldn't find the API that would fit the bill.
      Added comments to explain myself.

[V2]
    https://lore.kernel.org/all/20240514224508.212318-1-romank@linux.microsoft.com/
    - Decreased number of #ifdef's
    - Updated the wording in the commit messages to adhere to the guidlines
    - Sending to the correct set of maintainers and mail lists

[V1]
    https://lore.kernel.org/all/20240510160602.1311352-1-romank@linux.microsoft.com/

Roman Kisel (11):
  arm64: kvm, smccc: Introduce and use API for detectting hypervisor
    presence
  arm64: hyperv: Use SMCCC to detect hypervisor presence
  Drivers: hv: Enable VTL mode for arm64
  Drivers: hv: Provide arch-neutral implementation of get_vtl()
  arm64: hyperv: Initialize the Virtual Trust Level field
  arm64, x86: hyperv: Report the VTL the system boots in
  dt-bindings: microsoft,vmbus: Add interrupts and DMA coherence
  Drivers: hv: vmbus: Get the IRQ number from DeviceTree
  Drivers: hv: vmbus: Introduce hv_get_vmbus_root_device()
  ACPI: irq: Introduce acpi_get_gsi_dispatcher()
  PCI: hv: Get vPCI MSI IRQ domain from DeviceTree

 .../bindings/bus/microsoft,vmbus.yaml         |  8 +-
 arch/arm64/hyperv/mshyperv.c                  | 46 +++++++++--
 arch/arm64/kvm/hypercalls.c                   |  5 +-
 arch/x86/hyperv/hv_init.c                     | 34 --------
 arch/x86/hyperv/hv_vtl.c                      |  2 +-
 drivers/acpi/irq.c                            | 14 +++-
 drivers/firmware/smccc/kvm_guest.c            | 10 +--
 drivers/firmware/smccc/smccc.c                | 19 +++++
 drivers/hv/Kconfig                            | 10 ++-
 drivers/hv/hv_common.c                        | 31 ++++++++
 drivers/hv/vmbus_drv.c                        | 59 ++++++++++++--
 drivers/pci/controller/pci-hyperv.c           | 79 +++++++++++++++++--
 include/asm-generic/mshyperv.h                |  6 ++
 include/hyperv/hvgdk_mini.h                   |  2 +-
 include/linux/acpi.h                          |  5 +-
 include/linux/arm-smccc.h                     | 55 ++++++++++++-
 include/linux/hyperv.h                        |  2 +
 17 files changed, 308 insertions(+), 79 deletions(-)


base-commit: 3a7f7785eae7cf012af128ca9e383c91e4955354

On Fri, Mar 7, 2025, at 23:02, Roman Kisel wrote:
> @@ -5,18 +5,20 @@ menu "Microsoft Hyper-V guest support"
>  config HYPERV
>  	tristate "Microsoft Hyper-V client drivers"
>  	depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> -		|| (ACPI && ARM64 && !CPU_BIG_ENDIAN)
> +		|| (ARM64 && !CPU_BIG_ENDIAN)
> +	depends on (ACPI || HYPERV_VTL_MODE)
>  	select PARAVIRT
>  	select X86_HV_CALLBACK_VECTOR if X86
> -	select OF_EARLY_FLATTREE if OF
>  	help
>  	  Select this option to run Linux as a Hyper-V client operating
>  	  system.
> 
>  config HYPERV_VTL_MODE
>  	bool "Enable Linux to boot in VTL context"
> -	depends on X86_64 && HYPERV
> +	depends on (X86_64 || ARM64)
>  	depends on SMP
> +	select OF_EARLY_FLATTREE
> +	select OF
>  	default n
>  	help

Having the dependency below the top-level Kconfig entry feels a little
counterintuitive. You could flip that back as it was before by doing

      select HYPERV_VTL_MODE if !ACPI
      depends on ACPI || SMP

in the HYPERV option, leaving the dependency on HYPERV in
HYPERV_VTL_MODE.

Is OF_EARLY_FLATTREE actually needed on x86?

      Arnd