KVM: arm64: Handle FFA_FEATURES call from the host

Filter out advertising unsupported features, and only advertise
features and properties that are supported by the hypervisor proxy.

Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230523101828.7328-10-will@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Author: Fuad Tabba

arch/arm64/kvm/hyp/nvhe/ffa.c

@@ -64,15 +64,21 @@ static void ffa_to_smccc_error(struct arm_smccc_res *res, u64 ffa_errno)
 	};
 }
 
-static void ffa_to_smccc_res(struct arm_smccc_res *res, int ret)
+static void ffa_to_smccc_res_prop(struct arm_smccc_res *res, int ret, u64 prop)
 {
 	if (ret == FFA_RET_SUCCESS) {
-		*res = (struct arm_smccc_res) { .a0 = FFA_SUCCESS };
+		*res = (struct arm_smccc_res) { .a0 = FFA_SUCCESS,
+						.a2 = prop };
 	} else {
 		ffa_to_smccc_error(res, ret);
 	}
 }
 
+static void ffa_to_smccc_res(struct arm_smccc_res *res, int ret)
+{
+	ffa_to_smccc_res_prop(res, ret, 0);
+}
+
 static void ffa_set_retval(struct kvm_cpu_context *ctxt,
 			   struct arm_smccc_res *res)
 {
@@ -484,14 +490,41 @@ static bool ffa_call_supported(u64 func_id)
 	case FFA_RXTX_MAP:
 	case FFA_MEM_DONATE:
 	case FFA_MEM_RETRIEVE_REQ:
-	/* Don't advertise any features just yet */
-	case FFA_FEATURES:
 		return false;
 	}
 
 	return true;
 }
 
+static bool do_ffa_features(struct arm_smccc_res *res,
+			    struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, id, ctxt, 1);
+	u64 prop = 0;
+	int ret = 0;
+
+	if (!ffa_call_supported(id)) {
+		ret = FFA_RET_NOT_SUPPORTED;
+		goto out_handled;
+	}
+
+	switch (id) {
+	case FFA_MEM_SHARE:
+	case FFA_FN64_MEM_SHARE:
+	case FFA_MEM_LEND:
+	case FFA_FN64_MEM_LEND:
+		ret = FFA_RET_SUCCESS;
+		prop = 0; /* No support for dynamic buffers */
+		goto out_handled;
+	default:
+		return false;
+	}
+
+out_handled:
+	ffa_to_smccc_res_prop(res, ret, prop);
+	return true;
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(u64, func_id, host_ctxt, 0);
@@ -514,6 +547,10 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt)
 		return false;
 
 	switch (func_id) {
+	case FFA_FEATURES:
+		if (!do_ffa_features(&res, host_ctxt))
+			return false;
+		goto out_handled;
 	/* Memory management */
 	case FFA_FN64_RXTX_MAP:
 		do_ffa_rxtx_map(&res, host_ctxt);