[RFC PATCH 2/6] firmware: smccc: Detect hypervisor via RSI host call in CCA Realms

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

Modify arm_smccc_hypervisor_has_uuid() to check is_realm_world() and
use rsi_host_call() to query the hypervisor vendor UUID when inside a
Realm. The realm path is factored into a helper,
arm_smccc_realm_get_hypervisor_uuid(), that owns a file-static
rsi_host_call buffer (uuid_hc) serialized by a spinlock.

The RSI-specific includes, file-static state and helper are guarded
with CONFIG_ARM64 because <asm/rsi.h> does not exist on 32-bit ARM.

For non-Realm environments, the existing arm_smccc_1_1_invoke() path
is unchanged.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
---
 drivers/firmware/smccc/smccc.c | 41 +++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
index bdee057db2fd3..6b465e65472b0 100644
--- a/drivers/firmware/smccc/smccc.c
+++ b/drivers/firmware/smccc/smccc.c
@@ -12,6 +12,12 @@
 #include <linux/platform_device.h>
 #include <asm/archrandom.h>
 
+#ifdef CONFIG_ARM64
+#include <linux/cleanup.h>
+#include <linux/spinlock.h>
+#include <asm/rsi.h>
+#endif
+
 static u32 smccc_version = ARM_SMCCC_VERSION_1_0;
 static enum arm_smccc_conduit smccc_conduit = SMCCC_CONDUIT_NONE;
 
@@ -67,12 +73,45 @@ s32 arm_smccc_get_soc_id_revision(void)
 }
 EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_revision);
 
+#ifdef CONFIG_ARM64
+static struct rsi_host_call uuid_hc;
+static DEFINE_SPINLOCK(uuid_hc_lock);
+
+/*
+ * Helper function to get the hypervisor UUID via an RsiHostCall.
+ */
+static bool arm_smccc_realm_get_hypervisor_uuid(struct arm_smccc_res *res)
+{
+	guard(spinlock_irqsave)(&uuid_hc_lock);
+
+	memset(&uuid_hc, 0, sizeof(uuid_hc));
+	uuid_hc.gprs[0] = ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID;
+
+	if (rsi_host_call(__pa_symbol(&uuid_hc)) != RSI_SUCCESS)
+		return false;
+
+	res->a0 = uuid_hc.gprs[0];
+	res->a1 = uuid_hc.gprs[1];
+	res->a2 = uuid_hc.gprs[2];
+	res->a3 = uuid_hc.gprs[3];
+	return true;
+}
+#endif
+
 bool arm_smccc_hypervisor_has_uuid(const uuid_t *hyp_uuid)
 {
 	struct arm_smccc_res res = {};
 	uuid_t uuid;
 
-	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
+#ifdef CONFIG_ARM64
+	if (is_realm_world()) {
+		if (!arm_smccc_realm_get_hypervisor_uuid(&res))
+			return false;
+	} else
+#endif
+		arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID,
+				     &res);
+
 	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
 		return false;
 
-- 
2.45.4