arm64: kvm, smccc: Introduce and use API for getting hypervisor UUID

The KVM/arm64 uses SMCCC to detect hypervisor presence. That code is
private, and it follows the SMCCC specification. Other existing and
emerging hypervisor guest implementations can and should use that
standard approach as well.

Factor out a common infrastructure that the guests can use, update KVM
to employ the new API. The central notion of the SMCCC method is the
UUID of the hypervisor, and the new API follows that.

No functional changes. Validated with a KVM/arm64 guest.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250428210742.435282-2-romank@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250428210742.435282-2-romank@linux.microsoft.com>

Author: romank-msft

arch/arm64/kvm/hypercalls.c

@@ -270,6 +270,7 @@ int kvm_smccc_call_handler(struct kvm_vcpu *vcpu)
 	u32 feature;
 	u8 action;
 	gpa_t gpa;
+	uuid_t uuid;
 
 	action = kvm_smccc_get_action(vcpu, func_id);
 	switch (action) {
@@ -355,10 +356,11 @@ int kvm_smccc_call_handler(struct kvm_vcpu *vcpu)
 			val[0] = gpa;
 		break;
 	case ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID:
-		val[0] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0;
-		val[1] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1;
-		val[2] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2;
-		val[3] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3;
+		uuid = ARM_SMCCC_VENDOR_HYP_UID_KVM;
+		val[0] = smccc_uuid_to_reg(&uuid, 0);
+		val[1] = smccc_uuid_to_reg(&uuid, 1);
+		val[2] = smccc_uuid_to_reg(&uuid, 2);
+		val[3] = smccc_uuid_to_reg(&uuid, 3);
 		break;
 	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
 		val[0] = smccc_feat->vendor_hyp_bmap;

drivers/firmware/smccc/kvm_guest.c

@@ -17,17 +17,11 @@ static DECLARE_BITMAP(__kvm_arm_hyp_services, ARM_SMCCC_KVM_NUM_FUNCS) __ro_afte
 
 void __init kvm_init_hyp_services(void)
 {
+	uuid_t kvm_uuid = ARM_SMCCC_VENDOR_HYP_UID_KVM;
 	struct arm_smccc_res res;
 	u32 val[4];
 
-	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
-		return;
-
-	arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
-	if (res.a0 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 ||
-	    res.a1 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 ||
-	    res.a2 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 ||
-	    res.a3 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3)
+	if (!arm_smccc_hypervisor_has_uuid(&kvm_uuid))
 		return;
 
 	memset(&res, 0, sizeof(res));

drivers/firmware/smccc/smccc.c

@@ -67,6 +67,23 @@ s32 arm_smccc_get_soc_id_revision(void)
 }
 EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_revision);
 
+bool arm_smccc_hypervisor_has_uuid(const uuid_t *hyp_uuid)
+{
+	struct arm_smccc_res res = {};
+	uuid_t uuid;
+
+	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);
+	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
+		return false;
+
+	uuid = smccc_res_to_uuid(res.a0, res.a1, res.a2, res.a3);
+	return uuid_equal(&uuid, hyp_uuid);
+}
+EXPORT_SYMBOL_GPL(arm_smccc_hypervisor_has_uuid);
+
 static int __init smccc_devices_init(void)
 {
 	struct platform_device *pdev;

include/linux/arm-smccc.h

@@ -7,6 +7,11 @@
 
 #include <linux/args.h>
 #include <linux/init.h>
+
+#ifndef __ASSEMBLY__
+#include <linux/uuid.h>
+#endif
+
 #include <uapi/linux/const.h>
 
 /*
@@ -107,10 +112,10 @@
 			   ARM_SMCCC_FUNC_QUERY_CALL_UID)
 
 /* KVM UID value: 28b46fb6-2ec5-11e9-a9ca-4b564d003a74 */
-#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0	0xb66fb428U
-#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1	0xe911c52eU
-#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2	0x564bcaa9U
-#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3	0x743a004dU
+#define ARM_SMCCC_VENDOR_HYP_UID_KVM UUID_INIT(\
+	0xb66fb428, 0xc52e, 0xe911, \
+	0xa9, 0xca, 0x4b, 0x56, \
+	0x4d, 0x00, 0x3a, 0x74)
 
 /* KVM "vendor specific" services */
 #define ARM_SMCCC_KVM_FUNC_FEATURES		0
@@ -348,6 +353,57 @@ s32 arm_smccc_get_soc_id_version(void);
  */
 s32 arm_smccc_get_soc_id_revision(void);
 
+#ifndef __ASSEMBLY__
+
+/*
+ * Returns whether a specific hypervisor UUID is advertised for the
+ * Vendor Specific Hypervisor Service range.
+ */
+bool arm_smccc_hypervisor_has_uuid(const uuid_t *uuid);
+
+static inline uuid_t smccc_res_to_uuid(u32 r0, u32 r1, u32 r2, u32 r3)
+{
+	uuid_t uuid = {
+		.b = {
+			[0]  = (r0 >> 0)  & 0xff,
+			[1]  = (r0 >> 8)  & 0xff,
+			[2]  = (r0 >> 16) & 0xff,
+			[3]  = (r0 >> 24) & 0xff,
+
+			[4]  = (r1 >> 0)  & 0xff,
+			[5]  = (r1 >> 8)  & 0xff,
+			[6]  = (r1 >> 16) & 0xff,
+			[7]  = (r1 >> 24) & 0xff,
+
+			[8]  = (r2 >> 0)  & 0xff,
+			[9]  = (r2 >> 8)  & 0xff,
+			[10] = (r2 >> 16) & 0xff,
+			[11] = (r2 >> 24) & 0xff,
+
+			[12] = (r3 >> 0)  & 0xff,
+			[13] = (r3 >> 8)  & 0xff,
+			[14] = (r3 >> 16) & 0xff,
+			[15] = (r3 >> 24) & 0xff,
+		},
+	};
+
+	return uuid;
+}
+
+static inline u32 smccc_uuid_to_reg(const uuid_t *uuid, int reg)
+{
+	u32 val = 0;
+
+	val |= (u32)(uuid->b[4 * reg + 0] << 0);
+	val |= (u32)(uuid->b[4 * reg + 1] << 8);
+	val |= (u32)(uuid->b[4 * reg + 2] << 16);
+	val |= (u32)(uuid->b[4 * reg + 3] << 24);
+
+	return val;
+}
+
+#endif /* !__ASSEMBLY__ */
+
 /**
  * struct arm_smccc_res - Result from SMC/HVC call
  * @a0-a3 result values from registers 0 to 3