"Cannot allocate memory" when boots a VM > 1TB memory

[Harry Lee]

Hi,

I can't boot a VM with a memory > 1TB:

    root@debian11:~# qemu-system-x86_64 -m 1027G -accel kvm -vnc :1
    qemu-system-x86_64: kvm_set_user_memory_region: KVM_SET_USER_MEMORY_REGION 
failed, slot=1, start=0x100000000, size=0x10000000000: Cannot allocate memory
    kvm_set_phys_mem: error registering slot: Cannot allocate memory
    Aborted

The qemu version is:

    QEMU emulator version 5.2.0 (Debian 1:5.2+dfsg-11+deb11u1)
    Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers

I had set `vm.overcommit_memory=1`, so the host's memory does not matter. (I 
have 128GB memory, and I had successfully boot a 1024G VM)

I also check the CPU:

    Address sizes:                   46 bits physical, 48 bits virtual

It should support memory > 1TB.

So I don't know why it shown `Cannot allocate memory`.

I also tried to compile the latest `qemu-6.2.0` and use it, but it also shows 
the same error.

    root@debian11:/home/vmtest/qemu-6.2.0/build# ./qemu-system-x86_64 --version
    QEMU emulator version 6.2.0
    Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developers
    root@debian11:/home/vmtest/qemu-6.2.0/build# ./qemu-system-x86_64 -m 1027G 
-accel kvm -vnc :1
    qemu-system-x86_64: kvm_set_user_memory_region: KVM_SET_USER_MEMORY_REGION 
failed, slot=1, start=0x100000000, size=0x10000000000: Cannot allocate memory
    kvm_set_phys_mem: error registering slot: Cannot allocate memory
    Aborted