1 files changed, 145 insertions, 0 deletions
diff --git a/kernel/source/paging.cpp b/kernel/source/paging.cpp
new file mode 100644
index 0000000..d8869fc
--- /dev/null
+++ b/kernel/source/paging.cpp
@@ -0,0 +1,145 @@
+#include <hilbert/kernel/utility.hpp>
+#include <hilbert/kernel/paging.hpp>
+
+//see also ../documentation/memory.txt
+
+extern "C" {
+  uint64_t __kernel_p4_paddr;
+}
+
+namespace hilbert::kernel::paging {
+
+  static constexpr uint64_t kernel_vram_start = 0xffffffffc0000000;
+  static constexpr uint64_t kernel_vram_end = 0xffffffffffe00000;
+  static constexpr uint64_t kernel_vram_pages =
+    (kernel_vram_end - kernel_vram_start) / 4096;
+  static constexpr uint64_t syscall_stack_bottom = 0xfffffffffff01000;
+  static constexpr uint64_t syscall_stack_top = 0xfffffffffffff000;
+  static constexpr uint64_t interrupt_stack_bottom = 0xffffffffffe01000;
+  static constexpr uint64_t interrupt_stack_top = 0xffffffffffeff000;
+
+  static constexpr uint64_t pram_pages = 1 << 23;
+  static uint64_t pram_usage_bitmap[pram_pages / 64];
+
+  void mark_all_pram_used() {
+    utility::mark_bitmap_region_one(pram_usage_bitmap, 0, pram_pages);
+  }
+
+  void mark_pram_region_free(uint64_t start_addr, uint64_t end_addr) {
+    utility::mark_bitmap_region_zero(
+      pram_usage_bitmap, start_addr / 4096,
+      utility::min(end_addr / 4096, pram_pages));
+  }
+
+  [[gnu::aligned(4096)]] uint64_t kernel_p4[512];
+  [[gnu::aligned(4096)]] uint64_t kernel_p3[512];
+  [[gnu::aligned(4096)]] uint64_t kernel_p2[512];
+  [[gnu::aligned(4096)]] uint64_t kernel_p1s[512 * 512];
+
+  uint64_t kernel_p4e;
+
+  uint64_t encode_pte(uint64_t addr, bool user, bool write, bool execute) {
+    return (addr & 0x0000ffffffffffff) | (execute ? 0 : (1ULL << 63))
+         | (user << 2) | (write << 1) | 1;
+  }
+
+  void init_kernel_page_tables(uint64_t kernel_offset) {
+    __kernel_p4_paddr = (uint64_t)kernel_p4 - kernel_offset;
+    for (int i = 0; i < 511; ++i)
+      kernel_p4[i] = 0;
+    kernel_p4e = encode_pte(
+      (uint64_t)kernel_p3 - kernel_offset, false, true, true);
+    kernel_p4[511] = kernel_p4e;
+    for (int i = 0; i < 511; ++i)
+      kernel_p3[i] = 0;
+    kernel_p3[511] = encode_pte(
+      (uint64_t)kernel_p2 - kernel_offset, false, true, true);
+    for (int i = 0; i < 512; ++i)
+      kernel_p2[i] = encode_pte(
+        (uint64_t)kernel_p1s + 4096 * i - kernel_offset, false, true, true);
+    for (int i = 0; i < 512 * 512; ++i)
+      kernel_p1s[i] = 0;
+  }
+
+  void map_kernel_page(
+      uint64_t paddr, uint64_t vaddr, bool write, bool execute) {
+    uint64_t i = (vaddr - kernel_vram_start) / 4096;
+    kernel_p1s[i] = encode_pte(paddr, false, write, execute);
+  }
+
+  void unmap_kernel_page(uint64_t vaddr) {
+    uint64_t i = (vaddr - kernel_vram_start) / 4096;
+    kernel_p1s[i] = 0;
+    asm volatile (
+      "mov %%cr3, %%rax\nmov %%rax, %%cr3" ::: "%rax"
+    );
+  }
+
+  uint64_t take_pram_page() {
+    for (uint64_t i = 0; i < pram_pages / 64; ++i)
+      if (~pram_usage_bitmap[i] != 0)
+        for (int j = 0; j < 64; ++j)
+          if (~pram_usage_bitmap[i] & (1ULL << j)) {
+            pram_usage_bitmap[i] |= (1ULL << j);
+            return 4096 * (i * 64 + j);
+          }
+    //TODO: handle error
+    return 0;
+  }
+
+  void map_kernel_stacks() {
+    for (uint64_t vaddr = syscall_stack_bottom;
+         vaddr < syscall_stack_top; vaddr += 4096)
+      map_kernel_page(take_pram_page(), vaddr, true, false);
+    for (uint64_t vaddr = interrupt_stack_bottom;
+         vaddr < interrupt_stack_top; vaddr += 4096)
+      map_kernel_page(take_pram_page(), vaddr, true, false);
+  }
+
+  uint64_t find_unmapped_vram_region(uint64_t page_count) {
+    uint64_t start = 0;
+    uint64_t len = 0;
+    for (uint64_t i = 0; i < kernel_vram_pages; ++i)
+      if (kernel_p1s[i] == 0) {
+        ++len;
+        if (len == page_count)
+          return start * 4096 + kernel_vram_start;
+      }
+      else {
+        start = i + 1;
+        len = 0;
+      }
+    //TODO: handle error
+    return 0;
+  }
+
+  void *map_new_kernel_pages(uint64_t count) {
+    uint64_t vaddr = find_unmapped_vram_region(count);
+    for (uint64_t i = 0; i < count; ++i)
+      map_kernel_page(take_pram_page(), vaddr + i * 4096, true, false);
+    return (void *)vaddr;
+  }
+
+  void map_new_kernel_page(uint64_t &vaddr_out, uint64_t &paddr_out) {
+    vaddr_out = find_unmapped_vram_region(1);
+    paddr_out = take_pram_page();
+    map_kernel_page(paddr_out, vaddr_out, true, false);
+  }
+
+  uint64_t get_used_vram_page_count() {
+    uint64_t count = 0;
+    for (uint64_t i = 0; i < kernel_vram_pages; ++i)
+      if (kernel_p1s[i] != 0)
+        ++count;
+    return count;
+  }
+
+  uint64_t get_free_pram_page_count() {
+    uint64_t used_count = 0;
+    for (uint64_t i = 0; i < pram_pages / 64; ++i)
+      for (uint64_t j = 0; j < 64; ++j)
+        used_count += (pram_usage_bitmap[i] >> j) & 1;
+    return pram_pages - used_count;
+  }
+
+}