[PATCH v6 2/6] arm64: hyperv: Detect Hyper-V via RSI host call in CCA Realms

[Kameron Carr <kameroncarr@linux.microsoft.com>]

When booting without ACPI, hyperv_detect_via_smccc() detects Hyper-V by
querying the SMCCC vendor hypervisor UID. In an Arm CCA Realm the SMCCC
call is handled by the RMM rather than by the hypervisor, so the
query never reaches Hyper-V and detection fails.

When running in a Realm, forward ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID
to the host with RSI_HOST_CALL instead, which is how Hyper-V hypercalls
are issued from a Realm.

This is done in the Hyper-V code rather than in the generic
arm_smccc_hypervisor_has_uuid() because the other users expect different
behavior.

hyperv_init() is an early_initcall and runs before the secondary CPUs
are brought up, so a single __initdata host call structure is used
without locking.

ACPI-based detection and non-Realm guests are unaffected.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
---
 arch/arm64/hyperv/mshyperv.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 4fdc26a..82572c5 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -11,6 +11,7 @@
 
 #include <linux/types.h>
 #include <linux/acpi.h>
+#include <linux/arm-rsi-cmds.h>
 #include <linux/export.h>
 #include <linux/errno.h>
 #include <linux/version.h>
@@ -60,6 +61,27 @@ static bool __init hyperv_detect_via_acpi(void)
 
 #endif
 
+/*
+ * In a Realm, the SMCCC call is handled by the RMM rather than by
+ * Hyper-V, so the vendor hypervisor UID query must be forwarded to the
+ * host with RSI_HOST_CALL, in the same way as hypercalls.
+ */
+static bool __init hyperv_realm_has_uuid(const uuid_t *hyperv_uuid)
+{
+	static struct rsi_host_call hc __initdata;
+	uuid_t uuid;
+
+	hc.gprs[0] = ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID;
+
+	if (rsi_host_call(__pa_symbol(&hc)) != RSI_SUCCESS ||
+	    hc.gprs[0] == SMCCC_RET_NOT_SUPPORTED)
+		return false;
+
+	uuid = smccc_res_to_uuid(hc.gprs[0], hc.gprs[1], hc.gprs[2],
+				 hc.gprs[3]);
+	return uuid_equal(&uuid, hyperv_uuid);
+}
+
 static bool __init hyperv_detect_via_smccc(void)
 {
 	uuid_t hyperv_uuid = UUID_INIT(
@@ -67,6 +89,9 @@ static bool __init hyperv_detect_via_smccc(void)
 		0x75, 0x6c, 0xef, 0x8e,
 		0x24, 0x70, 0x59, 0x16);
 
+	if (is_realm_world())
+		return hyperv_realm_has_uuid(&hyperv_uuid);
+
 	return arm_smccc_hypervisor_has_uuid(&hyperv_uuid);
 }
 
-- 
2.45.4