diff --git a/arm/Makefile.arm64 b/arm/Makefile.arm64
index 42e18e77..ab557f84 100644
--- a/arm/Makefile.arm64
+++ b/arm/Makefile.arm64
@@ -24,6 +24,7 @@ cstart.o = $(TEST_DIR)/cstart64.o
 cflatobjs += lib/arm64/processor.o
 cflatobjs += lib/arm64/spinlock.o
 cflatobjs += lib/arm64/gic-v3-its.o lib/arm64/gic-v3-its-cmd.o
+cflatobjs += lib/arm64/rsi.o
 
 OBJDIRS += lib/arm64
 
diff --git a/lib/arm/asm/rsi.h b/lib/arm/asm/rsi.h
new file mode 100644
index 00000000..d1f72c25
--- /dev/null
+++ b/lib/arm/asm/rsi.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Arm Limited.
+ * All rights reserved.
+ */
+#ifndef __ASMARM_RSI_H_
+#define __ASMARM_RSI_H_
+
+#include <stdbool.h>
+
+static inline bool is_realm(void)
+{
+	return false;
+}
+
+#endif /* __ASMARM_RSI_H_ */
diff --git a/lib/arm/setup.c b/lib/arm/setup.c
index 65d98e97..36d4d826 100644
--- a/lib/arm/setup.c
+++ b/lib/arm/setup.c
@@ -24,6 +24,7 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>
+#include <asm/rsi.h>
 #include <asm/smp.h>
 #include <asm/timer.h>
 #include <asm/psci.h>
@@ -244,6 +245,8 @@ void setup(const void *fdt, phys_addr_t freemem_start)
 	u32 fdt_size;
 	int ret;
 
+	arm_rsi_init();
+
 	assert(sizeof(long) == 8 || freemem_start < (3ul << 30));
 	freemem = (void *)(unsigned long)freemem_start;
 
diff --git a/lib/arm64/asm/processor.h b/lib/arm64/asm/processor.h
index 1c73ba32..320ebaef 100644
--- a/lib/arm64/asm/processor.h
+++ b/lib/arm64/asm/processor.h
@@ -114,6 +114,14 @@ static inline unsigned long get_id_aa64mmfr0_el1(void)
 #define ID_AA64MMFR0_TGRAN64_SUPPORTED	0x0
 #define ID_AA64MMFR0_TGRAN16_SUPPORTED	0x1
 
+static inline unsigned long get_id_aa64pfr0_el1(void)
+{
+	return read_sysreg(id_aa64pfr0_el1);
+}
+
+#define ID_AA64PFR0_EL1_EL3	(0xf << 12)
+#define ID_AA64PFR0_EL1_EL3_NI	(0x0 << 12)
+
 static inline bool system_supports_granule(size_t granule)
 {
 	u32 shift;
diff --git a/lib/arm64/asm/rsi.h b/lib/arm64/asm/rsi.h
new file mode 100644
index 00000000..8b9b91b2
--- /dev/null
+++ b/lib/arm64/asm/rsi.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Arm Limited.
+ * All rights reserved.
+ */
+#ifndef __ASMARM64_RSI_H_
+#define __ASMARM64_RSI_H_
+
+#include <stdbool.h>
+
+#include <asm/arm-smccc.h>
+#include <asm/io.h>
+#include <asm/smc-rsi.h>
+
+#define RSI_GRANULE_SIZE	SZ_4K
+
+extern bool rsi_present;
+
+void arm_rsi_init(void);
+
+int rsi_invoke(unsigned int function_id, unsigned long arg0,
+	       unsigned long arg1, unsigned long arg2,
+	       unsigned long arg3, unsigned long arg4,
+	       unsigned long arg5, unsigned long arg6,
+	       unsigned long arg7, unsigned long arg8,
+	       unsigned long arg9, unsigned long arg10,
+	       struct smccc_result *result);
+
+int rsi_get_version(void);
+
+static inline bool is_realm(void)
+{
+	return rsi_present;
+}
+
+#endif /* __ASMARM64_RSI_H_ */
diff --git a/lib/arm64/rsi.c b/lib/arm64/rsi.c
new file mode 100644
index 00000000..23a4e963
--- /dev/null
+++ b/lib/arm64/rsi.c
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Arm Limited.
+ * All rights reserved.
+ */
+#include <libcflat.h>
+
+#include <asm/pgtable.h>
+#include <asm/processor.h>
+#include <asm/rsi.h>
+
+bool rsi_present;
+
+int rsi_invoke(unsigned int function_id, unsigned long arg0,
+	       unsigned long arg1, unsigned long arg2,
+	       unsigned long arg3, unsigned long arg4,
+	       unsigned long arg5, unsigned long arg6,
+	       unsigned long arg7, unsigned long arg8,
+	       unsigned long arg9, unsigned long arg10,
+	       struct smccc_result *result)
+{
+	return arm_smccc_smc(function_id, arg0, arg1, arg2, arg3, arg4, arg5,
+			     arg6, arg7, arg8, arg9, arg10, result);
+}
+
+struct rsi_realm_config __attribute__((aligned(RSI_GRANULE_SIZE))) config;
+
+static unsigned long rsi_get_realm_config(struct rsi_realm_config *cfg)
+{
+	struct smccc_result res;
+
+	rsi_invoke(SMC_RSI_REALM_CONFIG, __virt_to_phys((unsigned long)cfg),
+		   0, 0, 0, 0, 0, 0, 0, 0, 0, 0, &res);
+
+	return res.r0;
+}
+
+int rsi_get_version(void)
+{
+	struct smccc_result res = {};
+	int ret;
+
+	if ((get_id_aa64pfr0_el1() & ID_AA64PFR0_EL1_EL3) == ID_AA64PFR0_EL1_EL3_NI)
+		return -1;
+
+	ret = rsi_invoke(SMC_RSI_ABI_VERSION, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		         &res);
+	if (ret)
+		return ret;
+
+	return res.r0;
+}
+
+void arm_rsi_init(void)
+{
+	if (rsi_get_version() != RSI_ABI_VERSION)
+		return;
+
+	if (rsi_get_realm_config(&config))
+		return;
+
+	rsi_present = true;
+
+	phys_mask_shift = (config.ipa_width - 1);
+	/* Set the upper bit of the IPA as the NS_SHARED pte attribute */
+	prot_ns_shared = (1UL << phys_mask_shift);
+}
