The arm64 Hyper-V startup path relies on ACPI to detect
running under a Hyper-V compatible hypervisor. That
doesn't work on non-ACPI systems.

Hoist the ACPI detection logic into a separate function,
use the new SMC added recently to Hyper-V to use in the
non-ACPI case.

Signed-off-by: Roman Kisel <redacted>
---
 arch/arm64/hyperv/mshyperv.c      | 36 ++++++++++++++++++++++++++-----
 arch/arm64/include/asm/mshyperv.h |  5 +++++
 2 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index b1a4de4eee29..341f98312667 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c

@@ -27,6 +27,34 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
 	return 0;
 }
 
+static bool hyperv_detect_via_acpi(void)
+{
+	if (acpi_disabled)
+		return false;
+#if IS_ENABLED(CONFIG_ACPI)
+	/* Hypervisor ID is only available in ACPI v6+. */
+	if (acpi_gbl_FADT.header.revision < 6)
+		return false;
+	return strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8) == 0;
+#else
+	return false;
+#endif
+}
+
+static bool hyperv_detect_via_smc(void)
+{
+	struct arm_smccc_res res = {};
+
+	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
+		return false;
+	arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
+
+	return res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 &&
+		res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 &&
+		res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 &&
+		res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3;
+}