merge(kernel): add a scheduler

Starting from this commit, we have the first working implementation of
a scheduler for our kernel.

This scheduler is a basic pre-emptive single processor round robin one.
There are many improvements possible, which will be added later.
For more information, please refer to the documentation.

Merges #14

Signed-off-by: Léo DUBOIN <[email protected]>

README.md

@@ -52,27 +52,32 @@ I try to keep the codebase well-documented. You can generate the full doc using
 $ doxygen docs/doxygen/Doxyfile # Requires you to also pull the git submodules
 ```
 
-## What's available ?
-
-- GDT segments
-- Interrupts
-- Logging
-- PIT & Timer
-
-## Things I'd like to learn/implement
+## Things I'd like to learn
 
 - [X] Interrupts
 - Memory management
     - [X] Paging
-    - [X] PMM (physical)
     - [X] VMM (virtual)
-- [ ] Scheduler
-- [ ] Filesystem
-- [ ] Syscalls
-- User interaction
-    - [X] Keyboard
+    - [ ] CoW
+    - [ ] Guard pages
+- Drivers
+    - [X] Timer
     - [ ] Mouse
-    - [ ] Screen
-- [ ] Porting an already existing program (Can it run DOOM?)
-- [ ] Multitasking
-- [ ] Semaphores
+    - [ ] Networking
+    - [ ] Loadable kernel modules
+- Scheduling
+    - [X] Multitasking
+    - [ ] Priority
+    - [ ] Multiprocessor
+- Filesystems
+    - [ ] ext2
+    - [ ] VFS
+- Userland
+    - [ ] context switching
+    - [ ] syscalls
+- Porting
+    - [ ] Load/Execute ELF programs
+    - [ ] Porting an already existing program (Can it run DOOM?)
+    - [ ] Dynamic ELF relocation
+- [ ] IPC
+- [ ] SMP

include/kernel/arch/i686/cpu.h

@@ -22,7 +22,7 @@
         ASM("movl %0, %%" #_reg : : "r"(value));      \
     }
 
-#define CPU_32BIT_REGISTERS cr0, cr1, cr2, cr3, cr4, esp, cs, ss
+#define CPU_32BIT_REGISTERS cr0, cr1, cr2, cr3, cr4, esp, cs, ds, es, fs, gs, ss
 
 MAP(READ_REGISTER_OPS, CPU_32BIT_REGISTERS, )
 MAP(WRITE_REGISTER_OPS, CPU_32BIT_REGISTERS, )
@@ -73,4 +73,8 @@ static ALWAYS_INLINE uint32_t inl(uint16_t port)
     return val;
 }
 
+static ALWAYS_INLINE void hlt(void)
+{
+    ASM("hlt");
+}
 #endif /* KERNEL_I686_UTILS_CPU_OPS_H */

include/kernel/arch/i686/gdt.h

@@ -65,7 +65,7 @@ typedef struct gdt_descriptor {
 } gdt_descriptor;
 
 /**
- * @struct gdt_tss Task State Segment
+ * @struct tss Task State Segment
  *
  * A Task State Segment (TSS) is a binary data structure specific to the IA-32
  * and x86-64 architectures.
@@ -74,7 +74,7 @@ typedef struct gdt_descriptor {
  *
  * @see https://wiki.osdev.org/Task_State_Segment
  */
-typedef struct PACKED gdt_tss {
+typedef struct PACKED tss {
     u16 link;
     u16 _reserved1;
     u32 esp0;
@@ -114,7 +114,7 @@ typedef struct PACKED gdt_tss {
     u16 _reserved12;
     u16 iopb;
     u32 ssp;
-} gdt_tss;
+} tss_t;
 
 /**
  * @union segment_selector
@@ -150,4 +150,7 @@ void gdt_load_segment(gdt_descriptor, u16 index);
 /** Print the content of the GDT and GDTR. */
 void gdt_log(void);
 
+/** Modify the kernel stack pointer inside the current TSS */
+void gdt_set_esp0(u32);
+
 #endif /* KERNEL_ARCH_I686_GDT_H */

include/kernel/arch/i686/interrupts.h

@@ -164,4 +164,14 @@ static inline void interrupts_enable(void)
     ASM("sti");
 }
 
+/* @brief Disable CPU interrupts
+ * @return Whether the interrupts where previously enabled
+ */
+static inline bool interrupts_test_and_disable(void)
+{
+    u32 eflags;
+    ASM("pushf; cli; popl %0" : "=r"(eflags)::"memory");
+    return boolean(eflags & 0x200); // flag: IF
+}
+
 #endif /* KERNEL_I686_INTERRUPTS_H */

include/kernel/arch/i686/process.h

@@ -0,0 +1,35 @@
+#pragma once
+
+/**
+ * @file kernel/arch/i686/process.h
+ *
+ * @defgroup x86_process Processes - x86
+ * @ingroup process
+ * @ingroup x86
+ *
+ * @{
+ */
+
+#include <kernel/types.h>
+
+/**
+ * Contains all the system-level information about a task
+ * @struct x86_process
+ */
+typedef struct x86_process {
+
+    u32 cr3; ///< Physical address of the process's page directory
+
+    /**
+     * @brief Address of the top of the process's kernel stack.
+     *
+     * This is the value used by the kernel to locate the
+     * stack to use when switching from ring3 -> ring0.
+     * It should be loaded inside the current cpu's
+     * @link tss TSS.ESP0 @endlink when switching process.
+     */
+    u32 esp0;
+
+    u32 esp; ///< The current stack pointer of the process
+
+} process_context_t;

include/kernel/devices/timer.h

@@ -20,7 +20,7 @@
 
 #include <kernel/types.h>
 
-/** The frequency used for the timer (in KHz) */
+/** The frequency used for the timer (in Hz) */
 #define TIMER_TICK_FREQUENCY (1000) // 1KHz
 
 /**

include/kernel/error.h

@@ -23,8 +23,9 @@
  */
 typedef enum error {
     E_NONE,       ///< No error
+    E_NOMEM = 12, ///< Out of memory
     E_INVAL = 22, ///< Invalid argument
 } error_t;
 
 /** Check if an integer can be interpreted as an error */
-#define IS_ERR(_x) ((_x) < 0)
+#define IS_ERR(_x) ((s32)(_x) < 0)

include/kernel/interrupts.h

@@ -29,9 +29,14 @@
 
 #ifndef INLINED_INTERRUPTS_DISABLE_ENABLE
 
-/**@brief Disable CPU interrupts */
+/** @brief Disable CPU interrupts */
 void interrupts_disable(void);
 
+/* @brief Disable CPU interrupts
+ * @return Whether the interrupts where previously enabled
+ */
+bool interrupts_test_and_disable(void);
+
 /**@brief Enable CPU interrupts */
 void interrupts_enable(void);
 

include/kernel/kmalloc.h

@@ -57,6 +57,7 @@
  */
 typedef enum kmalloc_flags {
     KMALLOC_DEFAULT = 0x0, ///< Default
+    KMALLOC_KERNEL = 0x8,  ///< Use kernel pages only (@ref VMA_KERNEL)
 } kmalloc_flags;
 
 /**

include/kernel/logger.h

@@ -67,11 +67,13 @@ void log(const char *type, const char *domain, const char *msg, ...);
 void panic(u32 esp, const char *msg, ...) __attribute__((__noreturn__));
 
 /** @brief Call the panic function with the appropriate parameters */
-#define PANIC(...)               \
-    do {                         \
-        u32 esp = read_esp();    \
-        panic(esp, __VA_ARGS__); \
-    } while (0)
+#define PANIC(...)                   \
+    {                                \
+        do {                         \
+            u32 esp = read_esp();    \
+            panic(esp, __VA_ARGS__); \
+        } while (0);                 \
+    }
 
 // TODO: LOG_LEVEL filter
 

include/kernel/memory.h

@@ -12,19 +12,34 @@
  *
  *      0xFFFF_FFFF --------------------
  *                  |                  |
+ *                  |    Page Tables   |
+ *      0xFFC0_0000 |------------------|
+ *                  |      Kernel      |
+ *                  |   VMM Reserved   |
+ *      0xFFB0_0000 |------------------|
+ *                  |                  |
+ *                  |                  |
+ *                  |                  |
  *                  |  Kernel Memory   |
  *                  |                  |
+ *                  |                  |
+ *                  |                  |
  *      0xC000_0000 |------------------|
  *                  |                  |
  *                  |                  |
+ *                  |                  |
+ *                  |                  |
  *                  |       ...        |
  *                  |                  |
  *                  |                  |
+ *                  |                  |
+ *                  |                  |
+ *                  |                  |
  *      0x0110_0000 |------------------|
- *                  |  VMM Reserved    |
+ *                  |   VMM Reserved   |
  *      0x0100_0000 |------------------|
  *                  |     Reserved     |
- *      0x0000_0000 |------------------|
+ *      0x0000_0000 --------------------
  *
  * @{
  */
@@ -103,6 +118,22 @@ extern u32 _kernel_code_end;
 
 #endif /* __ASSEMBLER__ */
 
+#define PAGE_TABLES_START (0xFFC00000)
+
+/** @brief Location of the reserved range for the kernel's VMM structure
+ *  @ref kernel_vmm
+ *  @{
+ */
+#define KERNEL_VMM_RESERVED_END (PAGE_TABLES_START)
+#define KERNEL_VMM_RESERVED_START (KERNEL_VMM_RESERVED_END - VMM_RESERVED_SIZE)
+/** @} */
+
+#define KERNEL_MEMORY_END (KERNEL_VMM_RESERVED_START)
+#define KERNEL_MEMORY_START (KERNEL_CODE_END)
+
+#define USER_MEMORY_END KERNEL_MEMORY_START
+#define USER_MEMORY_START VMM_RESERVED_END
+
 /**
  * @brief Size of the area reserved fo rallovation memory management structures
  *

include/kernel/mmu.h

@@ -38,17 +38,30 @@ typedef enum mmu_prot {
     PROT_WRITE = 0x4, /*!< Pages may be written */
 } mmu_prot;
 
-/** @brief Inititialize the MMU's underlying structures */
-bool mmu_init(void);
-
-/**
- * @brief Enable paging and automatic virtual address translation.
+/** Initialize the MMU's paging system
+ *
+ * This function is responsible for setting any required bit inside the CPU's
+ * register.
  *
- * @warning After calling this function, each and every address will
+ * It is also responsible of remapping the kernel's code and addresses before
+ * enabling paging.
+ *
+ * @warning  After calling this function, each and every address will
  * automatically be translated into its physical equivalent using the paging
  * mechanism. Be sure to remap known addresses to avoid raising exceptions.
  */
-bool mmu_start_paging(void);
+bool mmu_init(void);
+
+/** @brief Inititialize a new page directory
+ *  @return The physical address of the new page_directory, 0 if error.
+ */
+paddr_t mmu_new_page_directory(void);
+
+/**
+ * @brief Replace the current page directory.
+ * @param page_directory The physical address of the page directory
+ */
+void mmu_load_page_directory(paddr_t);
 
 /**
  * @brief Map a virtual address to a physical one
@@ -89,4 +102,9 @@ paddr_t mmu_unmap(vaddr_t virt);
  */
 void mmu_identity_map(paddr_t start, paddr_t end, int prot);
 
+/** Find the physical mapping of a virtual address
+ *  @return -E_INVAL if error, a physical address if none
+ */
+paddr_t mmu_find_physical(vaddr_t);
+
 #endif /* KERNEL_MMU_H */