1 files changed, 129 insertions, 0 deletions
diff --git a/kernel/memory.c b/kernel/memory.c
new file mode 100644
index 0000000..465b44f
--- /dev/null
+++ b/kernel/memory.c
@@ -0,0 +1,129 @@
+#include <kernel/memory.h>
+#include <stdint.h>
+#include <sys/types.h>
+
+static char __attribute__((aligned (4096))) mapped_page[4096];
+
+static pdir_t kpdir;
+
+ptab_t ktab;
+
+static ptab_t flow;
+static ptab_t fupp;
+
+void *alloc_physical_page(void) {
+  int i;
+  void *ret;
+
+  for(i = 0; i < PGENT; i++) {
+    if(flow[i] & 1) {
+      ret = (void*) (flow[i] & ~1);
+      flow[i] = 0;
+      return ret;
+    }
+
+    if(fupp[i] & 1) {
+      ret = (void*) (fupp[i] & ~1);
+      fupp[i] = 0;
+      return ret;
+    }
+  }
+
+  return NULL;
+}
+
+int free_physical_page(void *page) {
+  int i;
+  page = (void*) ((uint32_t) page & ~0xFFF);
+
+  for(int i = 0; i < PGENT; i++) {
+    if(!(flow[i] & 1)) {
+      flow[i] = (uint32_t) page | 1;
+      return 0;
+    }
+
+    if(!(fupp[i] & 1)) {
+      fupp[i] = (uint32_t) page | 1;
+      return 0;
+    }
+  }
+
+  return -1;
+}
+
+void *alloc_physical_pages(unsigned int n) {
+  void *p = NULL;
+  void *last = NULL;
+  void **page;
+
+  while(n--) {
+    p = alloc_physical_page();
+    if(p == NULL) {
+      page = &last;
+      while(*page) {
+	free_physical_page(*page);
+        page = *page;
+      }
+      return NULL;
+    }
+
+    map_page(p);
+    *((void**) mapped_page) = last;
+    last = p;
+  }
+
+  return p;
+}
+
+void *map_page(void *page) {
+  uint32_t p = (uint32_t) mapped_page;
+
+  /* enforce 4KB page alignment */
+  page = (void*) ((uint32_t) page & ~0xFFF);
+
+  ktab[(p >> 12) & 0x3FF] = (uint32_t) page | 0x003;
+  /*
+   * invalidate any cached entries for
+   * the mapped page window.
+   */
+  __asm__ ("invlpg %0" :: "m" (mapped_page));
+
+  return mapped_page;
+}
+
+void paging_init(void) {
+  int i;
+
+  /* empty the page directory */
+  for(i = 0; i < PGENT; i++)
+    kpdir[i] = 0;
+
+  /* populate the free page tables */
+  for(i = 0; i < PGENT; i++) {
+    /* populate the lower table */
+    flow[i] = (i << 12);
+    /* only pages >1MB can be allocated */
+    if(i >= 0x100)
+      flow[i] |= 0x001;
+    /* populate the upper table */
+    fupp[i] = ((i << 12) + 0x400000) | 0x001;
+  }
+
+  /* populate the kernel's page table */
+  for(i = 0; i < PGENT; i++) {
+    ktab[i] = 0;
+    if(i < 256)
+      ktab[i] = (i << 12) | 0x003;
+  }
+
+  /* populate the kernel's page directory */
+  kpdir[0] = ((pde_t) ktab) | 0x007;
+
+  __asm__ (
+      "mov %%eax, %%cr3\n"
+      "mov %%cr0, %%eax\n"
+      "or $0x80000000, %%eax\n"
+      "mov %%eax, %%cr0\n"
+      :: "a" (&kpdir)
+      :);
+}