MemoryManager: Reuse the existing mapping of physical memory that MMU has

kernel/src/arch/MMU.h

@@ -27,6 +27,8 @@ namespace MMU
         Yes = 1
     };
 
+    u64 translate_physical_address(u64 phys);
+
     Result<void> map(u64 virt, u64 phys, int flags, UseHugePages use_huge_pages);
     Result<u64> unmap(u64 virt);
     Result<u64> get_physical(u64 virt);

kernel/src/arch/x86_64/MMU.cpp

@@ -47,6 +47,11 @@ namespace MMU
         return (T)(g_physical_mapping_base + (u64)phys);
     }
 
+    u64 translate_physical_address(u64 phys)
+    {
+        return g_physical_mapping_base + phys;
+    }
+
     void switch_page_directory(PageDirectory* dir)
     {
         asm volatile("mov %0, %%cr3" : : "r"(dir));

kernel/src/memory/MemoryManager.cpp

@@ -103,20 +103,10 @@ namespace MemoryManager
         KernelVM::init();
         MMU::setup_initial_page_directory();
 
-        // NOTE: We force these operations to succeed, because if we can't map the frame bitmap to virtual memory
-        // there's no point in continuing.
-        auto bitmap_pages = g_frame_bitmap.lock()->size_in_bytes() / ARCH_PAGE_SIZE;
-
-        auto virtual_bitmap_base =
-            KernelVM::alloc_several_pages(bitmap_pages)
-                .expect_value("Unable to allocate virtual memory for the physical frame bitmap, cannot continue");
-
-        u64 phys = (u64)g_frame_bitmap.lock()->location();
-        map_frames_at(virtual_bitmap_base, phys, bitmap_pages, MMU::ReadWrite | MMU::NoExecute)
-            .expect_value("Unable to map the physical frame bitmap to virtual memory, cannot continue");
-
         auto frame_bitmap = g_frame_bitmap.lock();
+        u64 phys = (u64)frame_bitmap->location();
 
+        auto virtual_bitmap_base = MMU::translate_physical_address(phys);
         frame_bitmap->initialize((void*)virtual_bitmap_base, frame_bitmap->size_in_bytes());
     }