diff --git a/litebox_common_optee/src/lib.rs b/litebox_common_optee/src/lib.rs
index 66a24be35..234080651 100644
--- a/litebox_common_optee/src/lib.rs
+++ b/litebox_common_optee/src/lib.rs
@@ -2025,7 +2025,7 @@ impl From<&OpteeSmcArgsPage> for OpteeSmcArgs {
 /// OP-TEE SMC call arguments.
 #[derive(Clone, Copy, Default, FromBytes)]
 pub struct OpteeSmcArgs {
-    args: [usize; Self::NUM_OPTEE_SMC_ARGS],
+    pub args: [usize; Self::NUM_OPTEE_SMC_ARGS],
 }
 
 impl OpteeSmcArgs {
@@ -2050,6 +2050,19 @@ impl OpteeSmcArgs {
         }
     }
 
+    /// Get the shared memory reference and offset for the physical address of `OpteeMsgArgs`.
+    pub fn optee_regd_shm_ref_and_offset(&self) -> Result<(u64, usize), OpteeSmcReturnCode> {
+        // args[1]:args[2] contains the shared memory reference (pointer)
+        // and args[3] contains the offset within that shared memory.
+        if self.args[1] & 0xffff_ffff_0000_0000 == 0 && self.args[2] & 0xffff_ffff_0000_0000 == 0 {
+            let shm_ref = (self.args[1] << 32) | self.args[2];
+            let offset = self.args[3];
+            Ok((shm_ref as u64, offset))
+        } else {
+            Err(OpteeSmcReturnCode::EBadAddr)
+        }
+    }
+
     /// Set the return code of an OP-TEE SMC call
     pub fn set_return_code(&mut self, code: OpteeSmcReturnCode) {
         self.args[0] = code as usize;
@@ -2121,6 +2134,7 @@ pub enum OpteeSmcResult<'a> {
     CallWithArg {
         msg_args: Box<OpteeMsgArgs>,
         rpc_args: Option<Box<OpteeRpcArgs>>,
+        msg_args_phys_addr: u64,
     },
 }
 
diff --git a/litebox_runner_lvbs/src/lib.rs b/litebox_runner_lvbs/src/lib.rs
index ed6302601..ffe2a040d 100644
--- a/litebox_runner_lvbs/src/lib.rs
+++ b/litebox_runner_lvbs/src/lib.rs
@@ -417,10 +417,6 @@ fn optee_smc_handler(smc_args_addr: usize) -> OpteeSmcArgs {
     let Ok(mut smc_args) = (unsafe { smc_args_ptr.read_at_offset(0) }) else {
         return make_error_response(OpteeSmcReturnCode::EBadAddr);
     };
-    let Ok(msg_args_phys_addr) = smc_args.optee_msg_args_phys_addr() else {
-        smc_args.set_return_code(OpteeSmcReturnCode::EBadAddr);
-        return *smc_args;
-    };
     let Ok(smc_result) = handle_optee_smc_args(&mut smc_args) else {
         smc_args.set_return_code(OpteeSmcReturnCode::EBadCmd);
         return *smc_args;
@@ -428,6 +424,7 @@ fn optee_smc_handler(smc_args_addr: usize) -> OpteeSmcArgs {
     if let OpteeSmcResult::CallWithArg {
         msg_args,
         rpc_args: _,
+        msg_args_phys_addr,
     } = smc_result
     {
         let mut msg_args = *msg_args;
diff --git a/litebox_shim_optee/src/msg_handler.rs b/litebox_shim_optee/src/msg_handler.rs
index f0c70acf7..5ca6243aa 100644
--- a/litebox_shim_optee/src/msg_handler.rs
+++ b/litebox_shim_optee/src/msg_handler.rs
@@ -185,13 +185,38 @@ pub fn handle_optee_smc_args(
             Ok(OpteeSmcResult::CallWithArg {
                 msg_args,
                 rpc_args: None,
+                msg_args_phys_addr: msg_args_addr as u64,
             })
         }
-        OpteeSmcFunction::CallWithRpcArg | OpteeSmcFunction::CallWithRegdArg => {
+        OpteeSmcFunction::CallWithRpcArg => {
             let msg_args_addr = smc.optee_msg_args_phys_addr()?;
             let msg_args_addr: usize = msg_args_addr.truncate();
             let (msg_args, rpc_args) = read_optee_msg_args_from_phys(msg_args_addr, true)?;
-            Ok(OpteeSmcResult::CallWithArg { msg_args, rpc_args })
+            Ok(OpteeSmcResult::CallWithArg {
+                msg_args,
+                rpc_args,
+                msg_args_phys_addr: msg_args_addr as u64,
+            })
+        }
+        OpteeSmcFunction::CallWithRegdArg => {
+            // `OpteeMsgArgs` is located at the offset specified in args[3] within the shared memory region pointed by args[1]:args[2].
+            let (shm_ref, offset) = smc.optee_regd_shm_ref_and_offset()?;
+            let shm_info = shm_ref_map()
+                .get(shm_ref)
+                .ok_or(OpteeSmcReturnCode::EBadAddr)?;
+            let page_index = (shm_info.page_offset + offset) / PAGE_SIZE;
+            let offset_in_page = (shm_info.page_offset + offset) % PAGE_SIZE;
+            if page_index >= shm_info.page_addrs.len() {
+                return Err(OpteeSmcReturnCode::EBadAddr);
+            }
+            let msg_args_addr = shm_info.page_addrs[page_index].as_usize() + offset_in_page;
+
+            let (msg_args, rpc_args) = read_optee_msg_args_from_phys(msg_args_addr, true)?;
+            Ok(OpteeSmcResult::CallWithArg {
+                msg_args,
+                rpc_args,
+                msg_args_phys_addr: msg_args_addr as u64,
+            })
         }
         OpteeSmcFunction::ExchangeCapabilities => {
             // TODO: update the below when we support more features