Comment 16 for bug 1769053

* Daniel Berrange (<email address hidden>) wrote:
> Hmm, if we know that QEMU guests will crash & burn when > 1 TB mem, when
> host-phys-bits/phys-bits are unset, then perhaps libvirt should do the
> right thing by default here. eg we can't use host-phys-bits=true due to
> migration compat issues, but if we see > 1TB mem, libvirt could
> reasonably set phys-bits=NNN for some suitable value of NNN. We should
> expose this in the XML config for the CPU explicitly too.

Yep:
  a) It should be possible to add a setting to the XML to specify the
     phys-bits
  b) It should be possible for libvirt to check the host it's on can
     satisfy that requirement
  c) libvirt can check that if RAM > 2^phys-bits it can complain

but

  d) For smaller amount of RAM it might still fail if
RAM+rounding+pci+hotplug space goes over the limit.
     Figuring that limit out is tricky (and I thought it
     might be BIOS/EFI dependent as well depending where they
     decide to put their PCI devices)

Dave

> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1769053
>
> Title:
> Cannot start a guest with more than 1TB of RAM
>
> Status in QEMU:
> Incomplete
> Status in qemu package in Ubuntu:
> Incomplete
>
> Bug description:
> Attempting to start a KVM guest with more than 1TB of RAM fails.
>
> It looks like we might need some extra patches:
> https://lists.gnu.org/archive/html/qemu-discuss/2017-12/msg00005.html
>
> ProblemType: Bug
> DistroRelease: Ubuntu 18.04
> Package: qemu-system-x86 1:2.11+dfsg-1ubuntu7
> ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
> Uname: Linux 4.15.0-20-generic x86_64
> ApportVersion: 2.20.9-0ubuntu7
> Architecture: amd64
> CurrentDesktop: Unity:Unity7:ubuntu
> Date: Fri May 4 16:21:14 2018
> InstallationDate: Installed on 2017-04-05 (393 days ago)
> InstallationMedia: Ubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.2)
> MachineType: Dell Inc. XPS 13 9360
> ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.15.0-20-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash transparent_hugepage=madvise vt.handoff=1
> SourcePackage: qemu
> UpgradeStatus: Upgraded to bionic on 2018-04-30 (3 days ago)
> dmi.bios.date: 02/26/2018
> dmi.bios.vendor: Dell Inc.
> dmi.bios.version: 2.6.2
> dmi.board.name: 0PF86Y
> dmi.board.vendor: Dell Inc.
> dmi.board.version: A00
> dmi.chassis.type: 9
> dmi.chassis.vendor: Dell Inc.
> dmi.modalias: dmi:bvnDellInc.:bvr2.6.2:bd02/26/2018:svnDellInc.:pnXPS139360:pvr:rvnDellInc.:rn0PF86Y:rvrA00:cvnDellInc.:ct9:cvr:
> dmi.product.family: XPS
> dmi.product.name: XPS 13 9360
> dmi.sys.vendor: Dell Inc.
>
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--
Dr. David Alan Gilbert / <email address hidden> / Manchester, UK