[RFC PATCH 1/6] arm64: rsi: Add RSI host call structure and helper function

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

Add struct rsi_host_call to rsi_smc.h, which represents the host call
data structure used by the Realm Management Monitor (RMM) for the
RSI_HOST_CALL interface. The structure contains a 16-bit immediate field
and 31 general-purpose register values, aligned to 256 bytes as required
by the CCA RMM specification.

Add rsi_host_call() static inline wrapper in rsi_cmds.h that invokes
SMC_RSI_HOST_CALL with the physical address of the host call structure.
This will be used by Hyper-V guest code to route hypercalls through the
RSI interface when running inside an Arm CCA Realm.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
---
 arch/arm64/include/asm/rsi_cmds.h | 9 +++++++++
 arch/arm64/include/asm/rsi_smc.h  | 6 ++++++
 2 files changed, 15 insertions(+)

diff --git a/arch/arm64/include/asm/rsi_cmds.h b/arch/arm64/include/asm/rsi_cmds.h
index 2c8763876dfb7..83b4b1f598454 100644
--- a/arch/arm64/include/asm/rsi_cmds.h
+++ b/arch/arm64/include/asm/rsi_cmds.h
@@ -159,4 +159,13 @@ static inline unsigned long rsi_attestation_token_continue(phys_addr_t granule,
 	return res.a0;
 }
 
+static inline long rsi_host_call(phys_addr_t host_call_struct)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(SMC_RSI_HOST_CALL, host_call_struct, 0, 0, 0, 0, 0, 0,
+		      &res);
+	return res.a0;
+}
+
 #endif /* __ASM_RSI_CMDS_H */
diff --git a/arch/arm64/include/asm/rsi_smc.h b/arch/arm64/include/asm/rsi_smc.h
index e19253f96c940..ffea93340ed7f 100644
--- a/arch/arm64/include/asm/rsi_smc.h
+++ b/arch/arm64/include/asm/rsi_smc.h
@@ -142,6 +142,12 @@ struct realm_config {
 	 */
 } __aligned(0x1000);
 
+struct rsi_host_call {
+	u16 immediate;
+	u64 gprs[31];
+} __aligned(256);
+static_assert(sizeof(struct rsi_host_call) == 256);
+
 #endif /* __ASSEMBLER__ */
 
 /*
-- 
2.45.4