Small kernel heap for VMM internals, kmalloc/kfree

src/mem/paging/vmm.c

@@ -0,0 +1,66 @@
+/*
+The VMM (virtual memory manager) will have two roles:
+- mapping pages
+- unmapping pages
+in a specified virtual space
+
+compared to the PMM which allocs/frees 4kb frames ("physical pages").
+*/
+
+#include "vmm.h"
+#include "paging.h"
+#include <stddef.h>
+#include "pmm.h"
+#include <kernel.h>
+
+void* vmm_pt_root = 0;
+
+// Linked list head for virtual memory objects
+struct vm_object* vm_objs = NULL;
+
+
+uint64_t convert_x86_vm_flags(size_t flags)
+{
+    uint64_t value = 0;
+    if (flags & VM_FLAG_WRITE)
+    {
+        value |= PTE_WRITABLE;
+    }
+    if (flags & VM_FLAG_USER)
+    {
+        value |= PTE_USER;
+    }
+    if ((flags & VM_FLAG_EXEC) == 0)
+    {
+        value |= PTE_NOEXEC;
+    }
+    return value;
+}
+
+extern uint64_t *kernel_pml4;
+
+void vmm_setup_pt_root()
+{
+    // We alloc a physical page (frame) for the pointer, then map it
+    // to virt (pointer)
+    uintptr_t phys = pmm_alloc();
+    vmm_pt_root = (void*)kernel_pml4;
+    paging_map_page(kernel_pml4, (uint64_t)vmm_pt_root, phys, convert_x86_vm_flags(VM_FLAG_WRITE | VM_FLAG_EXEC));
+    DEBUG("VMM setup: vmm_pt_root=0x%p (phys=0x%p)", vmm_pt_root, phys);
+}
+
+void* vmm_alloc(size_t length, size_t flags)
+{
+    // We will try to allocate at least length bytes, which have to be rounded UP to
+    // the next page so its coherent with the PMM
+    size_t len = ALIGN_UP(length, PAGE_SIZE);
+
+    // Some linked list shenanigans will be here
+    // but for now we'd need some kheap to kmalloc the linked list items
+    // else we can't do it
+}
+
+void vmm_init()
+{
+    vmm_setup_pt_root();
+}