firmware: qcom: scm: initialize tzmem before marking SCM as available

commit 87be3e7 upstream.

Now that qcom_scm_shm_bridge_enable() uses the struct device passed to
it as argument to make the QCOM_SCM_MP_SHM_BRIDGE_ENABLE SCM call, we
can move the TZMem initialization before the assignment of the __scm
pointer in the SCM driver (which marks SCM as ready to users) thus
fixing the potential race between consumer calls and the memory pool
initialization.

Reported-by: Johan Hovold <johan+linaro@kernel.org>
Closes: https://lore.kernel.org/all/20250120151000.13870-1-johan+linaro@kernel.org/
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20250630-qcom-scm-race-v2-3-fa3851c98611@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Bartosz Golaszewski

drivers/firmware/qcom/qcom_scm.c

@@ -2256,7 +2256,32 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	/* Paired with smp_load_acquire() in qcom_scm_is_available(). */
+	ret = of_reserved_mem_device_init(scm->dev);
+	if (ret && ret != -ENODEV)
+		return dev_err_probe(scm->dev, ret,
+				     "Failed to setup the reserved memory region for TZ mem\n");
+
+	ret = qcom_tzmem_enable(scm->dev);
+	if (ret)
+		return dev_err_probe(scm->dev, ret,
+				     "Failed to enable the TrustZone memory allocator\n");
+
+	memset(&pool_config, 0, sizeof(pool_config));
+	pool_config.initial_size = 0;
+	pool_config.policy = QCOM_TZMEM_POLICY_ON_DEMAND;
+	pool_config.max_size = SZ_256K;
+
+	scm->mempool = devm_qcom_tzmem_pool_new(scm->dev, &pool_config);
+	if (IS_ERR(scm->mempool))
+		return dev_err_probe(scm->dev, PTR_ERR(scm->mempool),
+				     "Failed to create the SCM memory pool\n");
+
+	/*
+	 * Paired with smp_load_acquire() in qcom_scm_is_available().
+	 *
+	 * This marks the SCM API as ready to accept user calls and can only
+	 * be called after the TrustZone memory pool is initialized.
+	 */
 	smp_store_release(&__scm, scm);
 
 	irq = platform_get_irq_optional(pdev, 0);
@@ -2289,32 +2314,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	if (of_property_read_bool(pdev->dev.of_node, "qcom,sdi-enabled") || !download_mode)
 		qcom_scm_disable_sdi();
 
-	ret = of_reserved_mem_device_init(__scm->dev);
-	if (ret && ret != -ENODEV) {
-		dev_err_probe(__scm->dev, ret,
-			      "Failed to setup the reserved memory region for TZ mem\n");
-		goto err;
-	}
-
-	ret = qcom_tzmem_enable(__scm->dev);
-	if (ret) {
-		dev_err_probe(__scm->dev, ret,
-			      "Failed to enable the TrustZone memory allocator\n");
-		goto err;
-	}
-
-	memset(&pool_config, 0, sizeof(pool_config));
-	pool_config.initial_size = 0;
-	pool_config.policy = QCOM_TZMEM_POLICY_ON_DEMAND;
-	pool_config.max_size = SZ_256K;
-
-	__scm->mempool = devm_qcom_tzmem_pool_new(__scm->dev, &pool_config);
-	if (IS_ERR(__scm->mempool)) {
-		ret = dev_err_probe(__scm->dev, PTR_ERR(__scm->mempool),
-				    "Failed to create the SCM memory pool\n");
-		goto err;
-	}
-
 	/*
 	 * Initialize the QSEECOM interface.
 	 *