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

Roman Kisel
2025-03-07T22:03:06Z

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
--
2.43.0