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[Christian Borntraeger <borntraeger@xxxxxxxxxx>]

the TCG emulation of QEMU does work without allocatr_pgste. 
vm.allocate_pgste=1 is necessary to use the KVM kernel module (which is used by qemu in kvm mode)

The main difference is that this uses 4k page tables instead of 2k page
tables on s390. So enabling pgstes will increase the page table
overhead. The difference is usually pretty small, but might become
noticeable when you have things like a big database with hundreds of
processes accessing a big area of shared memory.

Maybe something like
# cat /etc/modprobe.d/99-kvm.conf 
install kvm /sbin/sysctl vm.allocate_pgste=1; /sbin/modprobe --ignore-install kvm
remove kvm /sbin/sysctl vm.allocate_pgste=0; /sbin/modprobe -r --ignore-remove kvm

would be good enough?

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https://bugs.launchpad.net/bugs/1533646

Title:
  Could you set vm.allocate_pgste = 1 by default?

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Hello,

  to use qemu one needs  vm.allocate_pgste = 1, on kernels that support that setting e.g. s390x.
  I'm now setting it with a sysctl.d snippet in procps package, however I was wondering if it could be set by default.

  Or not.

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