efi: Implement reset_system for Cloud Hypervisor

The ResetSystem runtime service was intentionally left as a no-op
to force Linux to use ACPI for shutdown. However, Windows calls
ResetSystem(EfiResetShutdown) as its final shutdown step and does
not fall back to ACPI when the call returns. This causes the
Cloud Hypervisor process to hang indefinitely after Windows shuts
down.

Write the appropriate value to Cloud Hypervisor's shutdown I/O
port (0x600) based on the reset type:
- EfiResetShutdown: SLP_TYP=5 + SLP_EN (triggers VM exit)
- EfiResetCold/Warm: reboot value (triggers VM reset)

Linux guests are unaffected as they use ACPI directly.

Fixes: #422

Signed-off-by: CMGS <ilskdw@gmail.com>

Author: CMGS

src/efi/runtime_services.rs

@@ -196,8 +196,30 @@ pub extern "efiapi" fn get_next_high_mono_count(_: *mut u32) -> Status {
     Status::DEVICE_ERROR
 }
 
-pub extern "efiapi" fn reset_system(_: ResetType, _: Status, _: usize, _: *mut c_void) {
-    // Don't do anything to force the kernel to use ACPI for shutdown and triple-fault for reset
+pub extern "efiapi" fn reset_system(_reset_type: ResetType, _: Status, _: usize, _: *mut c_void) {
+    #[cfg(target_arch = "x86_64")]
+    {
+        // Cloud Hypervisor's AcpiShutdownDevice is at IO port 0x600.
+        const SHUTDOWN_PORT: u16 = 0x600;
+        const S5_SLEEP_VALUE: u8 = (5 << 2) | (1 << 5); // SLP_TYP=5, SLP_EN=1
+        const REBOOT_VALUE: u8 = 1;
+
+        let value = if _reset_type == efi::RESET_SHUTDOWN {
+            S5_SLEEP_VALUE
+        } else {
+            REBOOT_VALUE
+        };
+        unsafe {
+            core::arch::asm!("out dx, al", in("dx") SHUTDOWN_PORT, in("al") value);
+        }
+    }
+
+    loop {
+        #[cfg(target_arch = "x86_64")]
+        unsafe {
+            core::arch::asm!("hlt");
+        }
+    }
 }
 
 pub extern "efiapi" fn update_capsule(