feat(core/remote_io): add Remote I/O infrastructure

This commit introduces the foundational support for VirtIO by implementing
a mechanism to forward VirtIO requests bidirectionally between the
guest VM (or frontend VM) and its associated backend VM.

Signed-off-by: João Peixoto <joaopeixotooficial@gmail.com>

src/core/hypercall.c

@@ -20,6 +20,9 @@ long int hypercall(unsigned long id)
         case HC_IPC:
             ret = ipc_hypercall(arg0, arg1, arg2);
             break;
+        case HC_REMIO:
+            ret = remio_hypercall(arg0, arg1, arg2);
+            break;
         default:
             WARNING("Unknown hypercall id %d", id);
     }

src/core/inc/hypercall.h

@@ -9,7 +9,7 @@
 #include <bao.h>
 #include <arch/hypercall.h>
 
-enum { HC_INVAL = 0, HC_IPC = 1 };
+enum { HC_INVAL = 0, HC_IPC = 1, HC_REMIO = 2 };
 
 enum { HC_E_SUCCESS = 0, HC_E_FAILURE = 1, HC_E_INVAL_ID = 2, HC_E_INVAL_ARGS = 3 };
 

src/core/inc/remio.h

@@ -0,0 +1,87 @@
+/**
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ */
+
+/**
+ * @file remio.h
+ * @brief This header file contains the Remote I/O device interface
+ */
+
+#ifndef __REMIO_H__
+#define __REMIO_H__
+
+#include "types.h"
+#include <bao.h>
+#include <emul.h>
+#include <list.h>
+#include <vm.h>
+
+/**
+ * @struct remio_shmem
+ * @brief This structure represents a shared memory region used by a Remote I/O device
+ */
+struct remio_shmem {
+    paddr_t base;    /**< Shared memory base address */
+    size_t size;     /**< Shared memory size */
+    size_t shmem_id; /**< Shared memory ID */
+};
+
+/**
+ * @enum REMIO_DEV_TYPE
+ * @brief This enum represents the Remote I/O device type
+ */
+enum REMIO_DEV_TYPE {
+    REMIO_DEV_FRONTEND = 0, /**< Remote I/O frontend device */
+    REMIO_DEV_BACKEND       /**< Remote I/O backend device */
+};
+
+/**
+ * @struct remio_dev
+ * @brief This structure represents a Remote I/O device
+ * @note The device can be either a frontend (driver) or a backend (device)
+ */
+struct remio_dev {
+    vaddr_t va;               /**< Frontend MMIO base virtual address */
+    size_t size;              /**< Frontend MMIO size */
+    irqid_t interrupt;        /**< Frontend/backend interrupt number */
+    remio_id_t id;            /**< Remote I/O ID */
+    enum REMIO_DEV_TYPE type; /**< Type of the Remote I/O device */
+    struct remio_shmem shmem; /**< Shared memory region */
+};
+
+/**
+ * @brief Remote I/O device initialization routine
+ * @note Executed only once by the master CPU
+ */
+void remio_init(void);
+
+/**
+ * @brief Remote I/O device VM CPU assignment routine
+ * @note Executed by each VM that holds a Remote I/O device, it is responsible for
+ *       assigning the frontend or backend CPU ID for the respective Remote I/O device
+ *       If the VM was alloacted with more than one CPU the assigned CPU will be the
+ *       one with the lowest ID, since only one CPU is required to inject VM interrupts
+ * @param vm Pointer to the VM structure
+ */
+void remio_assign_vm_cpus(struct vm* vm);
+
+/**
+ * @brief Remote I/O hypercall callback
+ * @note Used to exchange information between the Remote I/O system and the backend VM
+ * @param arg0 First argument of the hypercall
+ * @param arg1 Second argument of the hypercall
+ * @param arg2 Third argument of the hypercall
+ * @return Returns the number of pending I/O requests
+ */
+long int remio_hypercall(unsigned long arg0, unsigned long arg1, unsigned long arg2);
+
+/**
+ * @brief Remote I/O MMIO emulation handler
+ * @note Executed by the frontend VM when a MMIO access is performed
+ * @param emul_access Holds the information about the MMIO access
+ * @return Returns true if handled successfully, false otherwise
+ */
+bool remio_mmio_emul_handler(struct emul_access* emul_access);
+
+#endif /* __REMIO_H__ */

src/core/inc/types.h

@@ -47,6 +47,8 @@ typedef unsigned irqid_t;
 
 typedef unsigned deviceid_t;
 
+typedef size_t remio_id_t;
+
 typedef enum AS_SEC {
     /*--- HYP AS SECTIONS -----*/
     SEC_HYP_GLOBAL = 0,

src/core/inc/vm.h

@@ -17,6 +17,7 @@
 #include <bitmap.h>
 #include <io.h>
 #include <ipc.h>
+#include <remio.h>
 
 struct vm_mem_region {
     paddr_t base;
@@ -47,6 +48,9 @@ struct vm_platform {
     size_t dev_num;
     struct vm_dev_region* devs;
 
+    size_t remio_dev_num;
+    struct remio_dev* remio_devs;
+
     // /**
     //  * In MPU-based platforms which might also support virtual memory
     //  * (i.e. aarch64 cortex-r) the hypervisor sets up the VM using an MPU by
@@ -84,6 +88,9 @@ struct vm {
 
     size_t ipc_num;
     struct ipc* ipcs;
+
+    size_t remio_dev_num;
+    struct remio_dev* remio_devs;
 };
 
 struct vcpu {

src/core/objects.mk

@@ -14,3 +14,4 @@ core-objs-y+=ipc.o
 core-objs-y+=objpool.o
 core-objs-y+=hypercall.o
 core-objs-y+=shmem.o
+core-objs-y+=remio.o