feat(aarch64): add WHP backend for ARM64 Windows

Implements the WHP hypervisor backend for aarch64, enabling Hyperlight
to run micro-VMs on Windows ARM64 systems with Hyper-V.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 6f20a05d-6bee-4e2e-b320-12f8d9759bbc
Signed-off-by: cshung <3410332+cshung@users.noreply.github.com>

Author: cshung

.github/workflows/WindowsArm64Smoke.yml

@@ -0,0 +1,42 @@
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
+
+name: Windows ARM64 Smoke Test
+
+on:
+  workflow_dispatch:
+  pull_request:
+
+env:
+  CARGO_TERM_COLOR: always
+  RUST_BACKTRACE: full
+
+permissions:
+  contents: read
+
+defaults:
+  run:
+    shell: pwsh
+
+jobs:
+  smoke:
+    runs-on: ["self-hosted", "Windows", "ARM64", "1ES.Pool=hl-windows-arm"]
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+
+      - name: Install Rust toolchain
+        run: |
+          rustup toolchain install 1.94 --profile minimal
+          rustup default 1.94
+
+      - name: Check environment
+        run: |
+          rustc --version
+          cargo --version
+          systeminfo | Select-String "OS Name","OS Version","System Type"
+
+      - name: Build hyperlight-host
+        run: cargo build -p hyperlight-host
+
+      - name: Run hyperlight-host tests
+        run: cargo test -p hyperlight-host

src/hyperlight_host/Cargo.toml

@@ -42,7 +42,6 @@ tracing-core = "0.1.36"
 tracing-opentelemetry = { version = "0.33.0", optional = true }
 hyperlight-common = { workspace = true, default-features = true, features = [ "std" ] }
 hyperlight-guest-tracing = { workspace = true, default-features = true, optional = true }
-vmm-sys-util = "0.15.0"
 crossbeam-channel = "0.5.15"
 thiserror = "2.0.18"
 chrono = { version = "0.4", optional = true }
@@ -84,6 +83,7 @@ kvm-bindings = { version = "0.14", features = ["fam-wrappers"], optional = true
 kvm-ioctls = { version = "0.25", optional = true }
 mshv-bindings = { version = "0.6", optional = true }
 mshv-ioctls = { version = "0.6", optional = true}
+vmm-sys-util = "0.15.0"
 
 [dev-dependencies]
 uuid = { version = "1.23.3", features = ["v4"] }

src/hyperlight_host/src/hypervisor/hyperlight_vm/aarch64.rs

@@ -35,10 +35,16 @@ use crate::hypervisor::regs::{CommonFpu, CommonRegisters, CommonSpecialRegisters
 use crate::hypervisor::virtual_machine::hvf::HvfVm;
 #[cfg(kvm)]
 use crate::hypervisor::virtual_machine::kvm::KvmVm;
+#[cfg(target_os = "windows")]
+use crate::hypervisor::virtual_machine::whp::WhpVm;
 use crate::hypervisor::virtual_machine::{
     HypervisorType, RegisterError, ResetVcpuError, VirtualMachine, VmError,
     get_available_hypervisor,
 };
+#[cfg(target_os = "linux")]
+use crate::hypervisor::LinuxInterruptHandle;
+#[cfg(target_os = "windows")]
+use crate::hypervisor::WindowsInterruptHandle;
 use crate::mem::mgr::{SandboxMemoryManager, SnapshotSharedMemory};
 use crate::mem::shared_mem::{GuestSharedMemory, HostSharedMemory};
 use crate::sandbox::SandboxConfiguration;
@@ -59,7 +65,7 @@ impl HyperlightVm {
         next_action: NextAction,
         rsp_gva: u64,
         page_size: usize,
-        config: &SandboxConfiguration,
+        #[cfg_attr(target_os = "windows", allow(unused_variables))] config: &SandboxConfiguration,
         #[cfg(gdb)] _gdb_conn: Option<DebugCommChannel<DebugResponse, DebugMsg>>,
         #[cfg(crashdump)] _rt_cfg: SandboxRuntimeConfig,
         #[cfg(feature = "mem_profile")] _trace_info: MemTraceInfo,
@@ -72,13 +78,14 @@ impl HyperlightVm {
         let mut vm: VmType = match get_available_hypervisor() {
             #[cfg(kvm)]
             Some(HypervisorType::Kvm) => Box::new(KvmVm::new().map_err(VmError::CreateVm)?),
-            // TODO: mshv support
             #[cfg(mshv3)]
             Some(HypervisorType::Mshv) => return Err(CreateHyperlightVmError::NoHypervisorFound),
             #[cfg(hvf)]
             Some(HypervisorType::Hvf) => {
                 Box::new(HvfVm::new(interrupt_handle.clone()).map_err(VmError::CreateVm)?)
             }
+            #[cfg(target_os = "windows")]
+            Some(HypervisorType::Whp) => Box::new(WhpVm::new().map_err(VmError::CreateVm)?),
             None => return Err(CreateHyperlightVmError::NoHypervisorFound),
         };
         vm.set_sregs(&CommonSpecialRegisters::defaults(root_pt_addr))
@@ -87,6 +94,10 @@ impl HyperlightVm {
         let interrupt_handle: Arc<dyn InterruptHandleImpl> =
             Arc::new(LinuxInterruptHandle::new(config));
 
+        #[cfg(target_os = "windows")]
+        let interrupt_handle: Arc<dyn InterruptHandleImpl> =
+            Arc::new(WindowsInterruptHandle::new(vm.partition_handle()));
+
         let snapshot_slot = 0u32;
         let scratch_slot = 1u32;
         let vm_can_reset_vcpu = vm.can_reset_vcpu();
@@ -206,7 +217,7 @@ impl HyperlightVm {
             self.vm_can_reset_vcpu,
             "No fallback path for vcpu reset on aarch64"
         );
-        self.vm.reset_vcpu()?;
+        self.interrupt_handle.reset_vcpu(self.vm.as_mut())?;
         self.apply_sregs(cr3, sregs)?;
         Ok(())
     }

src/hyperlight_host/src/hypervisor/mod.rs

@@ -45,6 +45,9 @@ use std::sync::atomic::{AtomicU8, Ordering};
 #[cfg(any(kvm, mshv3, hvf))]
 use std::time::Duration;
 
+#[cfg(target_arch = "aarch64")]
+use self::virtual_machine::{ResetVcpuError, VirtualMachine};
+
 #[derive(Debug)]
 pub(crate) struct InterruptHandleStateMachine(AtomicU8);
 impl InterruptHandleStateMachine {
@@ -142,6 +145,12 @@ pub(crate) trait InterruptHandleImpl: InterruptHandle {
 
     /// Mark the handle as dropped
     fn set_dropped(&self);
+
+    /// Reset the vCPU while honoring platform lifecycle synchronization.
+    #[cfg(target_arch = "aarch64")]
+    fn reset_vcpu(&self, vm: &mut dyn VirtualMachine) -> Result<(), ResetVcpuError> {
+        vm.reset_vcpu()
+    }
 }
 
 pub(crate) trait InterruptHandleInternal {
@@ -375,6 +384,20 @@ impl<T: SynchronousInterruptState> InterruptHandleImpl for SynchronousInterruptH
             }
         }
     }
+
+    #[cfg(target_arch = "aarch64")]
+    fn reset_vcpu(&self, vm: &mut dyn VirtualMachine) -> Result<(), ResetVcpuError> {
+        let guard = self
+            .dropped_state
+            .write()
+            .map_err(|e| ResetVcpuError::Unknown(e.to_string()))?;
+        if guard.0 {
+            return Err(ResetVcpuError::Unknown(
+                "cannot reset a dropped partition".to_string(),
+            ));
+        }
+        vm.reset_vcpu()
+    }
 }
 
 #[cfg(any(target_os = "windows", hvf))]

src/hyperlight_host/src/hypervisor/regs.rs

@@ -21,13 +21,13 @@ pub(crate) use x86_64::*;
 
 #[cfg(target_arch = "aarch64")]
 mod aarch64;
-#[cfg(target_os = "windows")]
+#[cfg(all(target_arch = "x86_64", target_os = "windows"))]
 use std::collections::HashSet;
 
 #[cfg(target_arch = "aarch64")]
 pub(crate) use aarch64::*;
 
-#[cfg(target_os = "windows")]
+#[cfg(all(target_arch = "x86_64", target_os = "windows"))]
 #[derive(Debug, PartialEq)]
 pub(crate) enum FromWhpRegisterError {
     MissingRegister(HashSet<i32>),