fix(core/remio): add device ready flag

This commit adds a device-ready flag to ensure that both backend and frontend
Remote I/O devices are fully initialized before the frontend initiates any
MMIO access. This flag prevents missed CPU messages from the frontend to the
backend in cases where the frontend (e.g., a bare-metal guest) initializes
and starts execution before the backend Remote I/O device is fully set up.

Signed-off-by: João Peixoto <[email protected]>

Author: joaopeixoto13

src/core/remio.c

@@ -95,7 +95,7 @@ struct remio_request_event {
 
 /**
  * @struct remio_device_config
- * @brief This structure holds the static information regarding a Remote I/O device
+ * @brief This structure holds the configuration of a Remote I/O device
  */
 struct remio_device_config {
     struct {
@@ -104,13 +104,15 @@ struct remio_device_config {
         vmid_t vm_id;              /**< Backend VM ID */
         irqid_t interrupt;         /**< Backend interrupt ID */
         struct remio_shmem shmem;  /**< Backend shared memory region */
+        bool ready;                /**< Backend ready flag */
     } backend;
     struct {
         remio_bind_key_t bind_key; /**< Frontend bind key */
         cpuid_t cpu_id;            /**< Frontend VM CPU ID */
         vmid_t vm_id;              /**< Frontend VM ID */
         irqid_t interrupt;         /**< Frontend interrupt ID */
         struct remio_shmem shmem;  /**< Frontend shared memory region */
+        bool ready;                /**< Frontend ready flag */
     } frontend;
 };
 
@@ -120,6 +122,7 @@ struct remio_device_config {
  */
 struct remio_device {
     node_t node;                                   /**< Node */
+    volatile bool ready;                           /**< Remote I/O device ready flag */
     remio_bind_key_t bind_key;                     /**< Remote I/O bind key */
     struct remio_device_config config;             /**< Remote I/O device configuration */
     struct list request_event_list;                /**< List of pending I/O requests events */
@@ -425,6 +428,7 @@ void remio_init(void)
                 if (device == NULL) {
                     ERROR("Failed creating Remote I/O device %d", dev->bind_key);
                 }
+                device->ready = false;
                 device->bind_key = dev->bind_key;
                 device->config.backend.bind_key = (remio_bind_key_t)-1;
                 device->config.frontend.bind_key = (remio_bind_key_t)-1;
@@ -434,9 +438,11 @@ void remio_init(void)
             if (dev->type == REMIO_DEV_BACKEND) {
                 device->config.backend.bind_key = dev->bind_key;
                 device->config.backend.shmem = dev->shmem;
+                device->config.backend.ready = false;
             } else if (dev->type == REMIO_DEV_FRONTEND) {
                 device->config.frontend.bind_key = dev->bind_key;
                 device->config.frontend.shmem = dev->shmem;
+                device->config.frontend.ready = false;
             } else {
                 ERROR("Unknown Remote I/O device type");
             }
@@ -496,9 +502,12 @@ void remio_assign_vm_cpus(struct vm* vm)
     list_foreach (remio_device_list, struct remio_device, dev) {
         if (vm->id == dev->config.backend.vm_id) {
             dev->config.backend.cpu_id = min(dev->config.backend.cpu_id, cpu()->id);
+            dev->config.backend.ready = true;
         } else if (vm->id == dev->config.frontend.vm_id) {
             dev->config.frontend.cpu_id = min(dev->config.frontend.cpu_id, cpu()->id);
+            dev->config.frontend.ready = true;
         }
+        dev->ready = dev->config.backend.ready && dev->config.frontend.ready;
     }
 }
 
@@ -671,6 +680,10 @@ bool remio_mmio_emul_handler(struct emul_access* acc)
         return false;
     }
 
+    /** Wait until the Remote I/O device is ready */
+    while (!device->ready)
+        ;
+
     /** Create a new Remote I/O request based on the MMIO access information */
     remio_create_request(acc, &request);