From 0f73efbdc329cac2b85a1ad6dbf6ec89ac9b0731 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Mon, 26 Oct 2020 20:17:08 -0400
Subject: [PATCH] add mm module to manage free physical page regions

---
 src/hos_main.c |  3 ++
 src/mbinfo.c   |  2 ++
 src/mm.c       | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++
 src/mm.h       | 11 ++++++++
 4 files changed, 90 insertions(+)
 create mode 100644 src/mm.c
 create mode 100644 src/mm.h

diff --git a/src/hos_main.c b/src/hos_main.c
index 0582d05..2ea1fd5 100644
--- a/src/hos_main.c
+++ b/src/hos_main.c
@@ -3,6 +3,7 @@
 #include "mbinfo.h"
 #include "klog.h"
 #include "gdt.h"
+#include "mm.h"
 
 void hos_main(uint32_t mbinfo_addr)
 {
@@ -17,5 +18,7 @@ void hos_main(uint32_t mbinfo_addr)
     }
     klog_init();
     klog_printf("Welcome to HOS!\n");
+    mm_init();
     mbinfo_load();
+    klog_printf("Found %dKB of usable RAM\n", mm_get_total_ram() / 1024u);
 }
diff --git a/src/mbinfo.c b/src/mbinfo.c
index b3739f2..9133410 100644
--- a/src/mbinfo.c
+++ b/src/mbinfo.c
@@ -3,6 +3,7 @@
 #include "mem.h"
 #include <stdint.h>
 #include "klog.h"
+#include "mm.h"
 
 static uint32_t mbinfo[2048];
 
@@ -46,6 +47,7 @@ static void mbinfo_process_tag(const multiboot2_info_tag_t * tag)
                     klog_printf("Memory region %16lx : %16lx\n",
                             entry->base_addr,
                             entry->length);
+                    mm_register_ram_region(entry->base_addr, entry->length);
                 }
                 entry = (multiboot2_info_memory_map_entry_t *)((uintptr_t)entry + mmap_info->entry_size);
             }
diff --git a/src/mm.c b/src/mm.c
new file mode 100644
index 0000000..39dc112
--- /dev/null
+++ b/src/mm.c
@@ -0,0 +1,74 @@
+#include "mm.h"
+#include "klog.h"
+
+#define PAGE_SIZE 4096u
+
+typedef struct mm_page_entry_s {
+    size_t count;
+    struct mm_page_entry_s * next;
+} mm_region_entry_t;
+
+static mm_region_entry_t * mm_next_free_region;
+static size_t mm_free_page_count;
+static size_t mm_total_ram;
+
+extern uint8_t _hos_mem_start;
+extern uint8_t _hos_mem_end;
+
+static void mm_add_ram_region(uint32_t base, uint32_t size)
+{
+    mm_region_entry_t * region = (mm_region_entry_t *)base;
+    size_t pages = size / PAGE_SIZE;
+    region->count = pages;
+    region->next = mm_next_free_region;
+    mm_next_free_region = region;
+    mm_total_ram += size;
+    mm_free_page_count = pages;
+}
+
+void mm_register_ram_region(uint64_t base, uint32_t size)
+{
+    size &= ~(PAGE_SIZE - 1u);
+    /* Ignore any RAM region above 4GB. */
+    if (base >= 0x100000000ull)
+    {
+        return;
+    }
+    if ((base + size) > 0x100000000ull)
+    {
+        size = (uint32_t)(0x100000000ull - base);
+    }
+    /* Add regions before and after kernel RAM. */
+    uint32_t region_base = (uint32_t)base;
+    if (region_base < (uint32_t)&_hos_mem_start)
+    {
+        /* RAM region begins before kernel RAM. */
+        uint32_t this_sz = size;
+        if ((region_base + this_sz) > (uint32_t)&_hos_mem_start)
+        {
+            this_sz = (uint32_t)&_hos_mem_start - region_base;
+        }
+        mm_add_ram_region(region_base, this_sz);
+    }
+    if ((region_base + size) > (uint32_t)&_hos_mem_end)
+    {
+        /* RAM region ends after kernel RAM. */
+        uint32_t this_sz = size;
+        if (region_base < (uint32_t)&_hos_mem_end)
+        {
+            this_sz = (region_base + size) - (uint32_t)&_hos_mem_end;
+            region_base = (uint32_t)&_hos_mem_end;
+        }
+        mm_add_ram_region(region_base, this_sz);
+    }
+}
+
+void mm_init(void)
+{
+    mm_total_ram = &_hos_mem_end - &_hos_mem_start;
+}
+
+size_t mm_get_total_ram(void)
+{
+    return mm_total_ram;
+}
diff --git a/src/mm.h b/src/mm.h
new file mode 100644
index 0000000..0661fa9
--- /dev/null
+++ b/src/mm.h
@@ -0,0 +1,11 @@
+#ifndef MM_H
+#define MM_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+void mm_init(void);
+void mm_register_ram_region(uint64_t base, uint32_t size);
+size_t mm_get_total_ram(void);
+
+#endif