Reload GDT with the descriptor VMA once the CPU switches to 64-bit mode
Reload GDT with the descriptor VMA once the CPU switches to 64-bit mode

The GDT is initially loaded in the 32-bit rt0 code where we cannot use
the 48-bit VMA for the GDT table and instead we use its physical
address. This approach works as the rt0 code establishes an identity
mapping for the region 0-8M. However, when the kernel creates a more
granular PDT it only includes the VMA addresses for the kernel ELF image
sections making the 0-8M invalid. Unless the GDT is reloaded with the
VMA of the table, the CPU will cause a non-recoverable page fault when
it tries to restore the segment registers while returning from a
recoverable page fault.

achilleasa/gopher-os,achilleasa/gopher-os