From guest VM that booted slowly, has 52 physbits/57 virtual bits, and in which GPU driver works correctly:

ubuntu@testbox01:~$ sudo cat /proc/iomem
00000000-00000fff : Reserved
00001000-0009ffff : System RAM
000a0000-000bffff : PCI Bus 0000:00
000f0000-000fffff : System ROM
00100000-7e326017 : System RAM
7e326018-7e358057 : System RAM
7e358058-7ed3efff : System RAM
7ed3f000-7edfffff : Reserved
7ee00000-7f8ecfff : System RAM
7f8ed000-7fb6cfff : Reserved
7fb6d000-7fb7efff : ACPI Tables
7fb7f000-7fbfefff : ACPI Non-volatile Storage
7fbff000-7ff7bfff : System RAM
7ff7c000-7fffffff : Reserved
80000000-dfffffff : PCI Bus 0000:00
  80000000-801fffff : PCI Bus 0000:0e
  80200000-803fffff : PCI Bus 0000:0d
  80400000-805fffff : PCI Bus 0000:0c
  80600000-807fffff : PCI Bus 0000:0b
    80600000-80600fff : 0000:0b:00.0
  80800000-809fffff : PCI Bus 0000:0a
  80a00000-80bfffff : PCI Bus 0000:09
  80c00000-80dfffff : PCI Bus 0000:08
  80e00000-80ffffff : PCI Bus 0000:07
  81000000-811fffff : PCI Bus 0000:06
  81200000-813fffff : PCI Bus 0000:05
    81200000-81200fff : 0000:05:00.0
  81400000-815fffff : PCI Bus 0000:04
    81400000-81400fff : 0000:04:00.0
  81600000-817fffff : PCI Bus 0000:03
    81600000-81600fff : 0000:03:00.0
  81800000-819fffff : PCI Bus 0000:02
    81800000-81803fff : 0000:02:00.0
      81800000-81803fff : xhci-hcd
  81a00000-81bfffff : PCI Bus 0000:01
    81a00000-81a00fff : 0000:01:00.0
    81a80000-81afffff : 0000:01:00.0
  81c80000-81c80fff : 0000:00:1f.2
    81c80000-81c80fff : ahci
  81c81000-81c81fff : 0000:00:02.5
  81c82000-81c82fff : 0000:00:02.4
  81c83000-81c83fff : 0000:00:02.3
  81c84000-81c84fff : 0000:00:02.2
  81c85000-81c85fff : 0000:00:02.1
  81c86000-81c86fff : 0000:00:02.0
  81c87000-81c87fff : 0000:00:01.7
  81c88000-81c88fff : 0000:00:01.6
  81c89000-81c89fff : 0000:00:01.5
  81c8a000-81c8afff : 0000:00:01.4
  81c8b000-81c8bfff : 0000:00:01.3
  81c8c000-81c8cfff : 0000:00:01.2
  81c8d000-81c8dfff : 0000:00:01.1
  81c8e000-81c8efff : 0000:00:01.0
e0000000-efffffff : PCI MMCONFIG 0000 [bus 00-ff]
  e0000000-efffffff : Reserved
    e0000000-efffffff : pnp 00:04
f0000000-febfffff : PCI Bus 0000:00
fec00000-fec003ff : IOAPIC 0
fed40000-fed40fff : MSFT0101:00
  fed40000-fed40fff : MSFT0101:00
fee00000-fee00fff : Local APIC
feffc000-feffffff : Reserved
ffc00000-ffffffff : Reserved
100000000-e6dfffffff : System RAM
  239ce00000-239de022c1 : Kernel code
  239e000000-239eab4fff : Kernel rodata
  239ec00000-239f04b4ff : Kernel data
  239f3bd000-23a05fffff : Kernel bss
380000000000-3937ffffffff : PCI Bus 0000:00
  380000000000-382002ffffff : PCI Bus 0000:06
    380000000000-381fffffffff : 0000:06:00.0
    382000000000-382001ffffff : 0000:06:00.0
    382002000000-382002ffffff : 0000:06:00.0
  384000000000-386002ffffff : PCI Bus 0000:07
    384000000000-385fffffffff : 0000:07:00.0
    386000000000-386001ffffff : 0000:07:00.0
    386002000000-386002ffffff : 0000:07:00.0
  388000000000-38a002ffffff : PCI Bus 0000:08
    388000000000-389fffffffff : 0000:08:00.0
    38a000000000-38a001ffffff : 0000:08:00.0
    38a002000000-38a002ffffff : 0000:08:00.0
  38c000000000-38e002ffffff : PCI Bus 0000:09
    38c000000000-38dfffffffff : 0000:09:00.0
    38e000000000-38e001ffffff : 0000:09:00.0
    38e002000000-38e002ffffff : 0000:09:00.0
  38e800000000-38efffffffff : PCI Bus 0000:01
    38e800000000-38e800003fff : 0000:01:00.0
      38e800000000-38e800003fff : virtio-pci-modern
  38f000000000-38f7ffffffff : PCI Bus 0000:02
  38f800000000-38ffffffffff : PCI Bus 0000:03
    38f800000000-38f800003fff : 0000:03:00.0
      38f800000000-38f800003fff : virtio-pci-modern
  390000000000-3907ffffffff : PCI Bus 0000:04
    390000000000-390000003fff : 0000:04:00.0
      390000000000-390000003fff : virtio-pci-modern
  390800000000-390fffffffff : PCI Bus 0000:05
    390800000000-390800003fff : 0000:05:00.0
      390800000000-390800003fff : virtio-pci-modern
  391000000000-3917ffffffff : PCI Bus 0000:0a
    391000000000-391000003fff : 0000:0a:00.0
      391000000000-391000003fff : virtio-pci-modern
  391800000000-391fffffffff : PCI Bus 0000:0b
    391800000000-391800003fff : 0000:0b:00.0
      391800000000-391800003fff : virtio-pci-modern
  392000000000-3927ffffffff : PCI Bus 0000:0c
  392800000000-392fffffffff : PCI Bus 0000:0d
  393000000000-3937ffffffff : PCI Bus 0000:0e