* Gerd Hoffmann (1769...@bugs.launchpad.net) wrote: > Hi, > > > 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) > > Both seabios and ovmf try to not go too high in address space. Reason > is exactly the phys-bits issue. Using 40 here by default does not only > limit the memory to 1TB. It also has the problem that the guest thinks > it has 1TB of address space but in reality it might be less. Even > recent skylake machines have phys-bits=39 (512G) only, and trying to use > the physical address space above 512G in the guest just doesn't work > because the phys-bits=39 limit applies to EPT too. > > So checking phys-bits in the firmware, for example to place pci bars as > high as possible in physical address space, is not going to work. > > IIRC ovmf uses a 32G sized region with 32G alignment by default, which > will land below 64G (aka phys-bits=36 address space) unless the guest > has more than 30 (q35) or 31 (piix4) GB of memory. > > seabios will not map pci bars above 4G unless it runs out of space below > 4G. If needed 64bit PCI bars will be placed right above ram, with > gigabyte alignment.
Yep, I was tempted to set host-phys-bits=true on upstream, but TCG has a fixed 40 bits last time I looked. Dave > cheers, > Gerd > > -- > 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. > > To manage notifications about this bug go to: > https://bugs.launchpad.net/qemu/+bug/1769053/+subscriptions -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1769053 Title: Cannot start a guest with more than 1TB of RAM To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1769053/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
