Comment 12 for bug 1685242

* From "debug-nonworking.log":

> GetFirstNonAddress: Pci64Base=0x8800000000 Pci64Size=0x800000000
> [...]
> PublishPeiMemory: mPhysMemAddressWidth=40 PeiMemoryCap=69644 KB
> [...]
> Type = Mem64; Base = 0x8800000000; Length = 0x100000; Alignment = 0xFFFFF
> Base = 0x8800000000; Length = 0x4000; Alignment = 0x3FFF; Owner = PCI [00|12|00:20]; Type = PMem64

- The 64-bit MMIO aperture starts at (512+32)GB (see "Pci64Base").
- 40 physical address bits are required (see "mPhysMemAddressWidth").
  Your PCPU has 39 (thanks for confirming that).
- The 64-bit MMIO BAR of the virtio-net-pci device is allocated at
  (512+32)GB. Will not be accessible.

* From "debug-working-222G.log":

> GetFirstNonAddress: Pci64Base=0x7800000000 Pci64Size=0x800000000
> [...]
> PublishPeiMemory: mPhysMemAddressWidth=39 PeiMemoryCap=67592 KB
> [...]
> Type = Mem64; Base = 0x7800000000; Length = 0x100000; Alignment = 0xFFFFF
> Base = 0x7800000000; Length = 0x4000; Alignment = 0x3FFF; Owner = PCI [00|12|00:20]; Type = PMem64

- Aperture at 480GB.
- 39 phys bits suffice.
- BAR allocated at 480GB. Will be accessible.

* From "debug-working-novirtio-net.log":

- Identical to "debug-nonworking.log", except there is no PCI device
  with a 64-bit BAR, hence no attempt is made to access the inaccessible
  aperture.

* Regarding why 222GB seems to be the cutoff. The base of the 64-bit
  aperture must be suitably aligned. I explained this in the
  earlier-referenced
  <https://bugzilla.redhat.com/show_bug.cgi?id=1353591#c8>, in
  particular, bullet (6). If you decrease the aperture size, the
  required alignment will shrink as well, and the DIMM hotplug cutoff
  might increase. Please refer to

    -fw_cfg name=opt/ovmf/X-PciMmio64Mb,string=4096

  in <https://bugzilla.redhat.com/show_bug.cgi?id=1353591#c10>.

Right now everything appears to work by design. Closing this ticket.