[PATCH hyperv-next v5 02/11] arm64: hyperv: Use SMCCC to detect hypervisor presence

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

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. Then
use the vendor-specific hypervisor service call (implemented
recently in Hyper-V) via SMCCC in the non-ACPI case.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
---
arch/arm64/hyperv/mshyperv.c | 43 +++++++++++++++++++++++++++++++-----
1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 29fcfd595f48..c647db56fd6b 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -27,6 +27,41 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
return 0;
}

+static bool __init hyperv_detect_via_acpi(void)
+{
+ if (acpi_disabled)
+ return false;
+#if IS_ENABLED(CONFIG_ACPI)
+ /*
+ * Hypervisor ID is only available in ACPI v6+, and the
+ * structure layout was extended in v6 to accommodate that
+ * new field.
+ *
+ * At the very minimum, this check makes sure not to read
+ * past the FADT structure.
+ *
+ * It is also needed to catch running in some unknown
+ * non-Hyper-V environment that has ACPI 5.x or less.
+ * In such a case, it can't be Hyper-V.
+ */
+ 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 __init hyperv_detect_via_smccc(void)
+{
+ uuid_t hyperv_uuid = UUID_INIT(
+ 0x4d32ba58, 0x4764, 0xcd24,
+ 0x75, 0x6c, 0xef, 0x8e,
+ 0x24, 0x70, 0x59, 0x16);
+
+ return arm_smccc_hyp_present(&hyperv_uuid);
+}
+
static int __init hyperv_init(void)
{
struct hv_get_vp_registers_output result;
@@ -35,13 +70,11 @@ static int __init hyperv_init(void)

/*
* Allow for a kernel built with CONFIG_HYPERV to be running in
- * a non-Hyper-V environment, including on DT instead of ACPI.
+ * a non-Hyper-V environment.
+ *
* In such cases, do nothing and return success.
*/
- if (acpi_disabled)
- return 0;
-
- if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
+ if (!hyperv_detect_via_acpi() && !hyperv_detect_via_smccc())
return 0;

/* Setup the guest ID */
--
2.43.0