HACK: hvf: arm: Always treat SMC as enabled conduit

The Windows 10 and 11 for ARM boot code implicitly assumes that SMC is a valid
SMCCC conduit to call for an OEM SMCCC call.

This patch forces HVF to treat SMC as an always active conduit, even when the
user has configured HVC. That way, the OEM SMCCC call gets handled as an
unimplemented SMCCC function (return -1) rather than an invalid conduit (inject
undefined instruction exception) which crashes Windows.

With this patch applied, I can successfully boot Windows for ARM Insider
Previews.

Signed-off-by: Alexander Graf <agraf@csgraf.de>

target/arm/hvf/hvf.c

@@ -61,6 +61,8 @@
 #define TMR_CTL_IMASK   (1 << 1)
 #define TMR_CTL_ISTATUS (1 << 2)
 
+static const bool windows_workaround_enabled = true;
+
 static void hvf_wfi(CPUState *cpu);
 
 typedef struct HVFVTimer {
@@ -1218,7 +1220,8 @@ int hvf_vcpu_exec(CPUState *cpu)
         break;
     case EC_AA64_SMC:
         cpu_synchronize_state(cpu);
-        if (arm_cpu->psci_conduit == QEMU_PSCI_CONDUIT_SMC) {
+        if (windows_workaround_enabled ||
+            arm_cpu->psci_conduit == QEMU_PSCI_CONDUIT_SMC) {
             advance_pc = true;
 
             if (!hvf_handle_psci_call(cpu)) {