KVM: s390: introduce module parameter kvm.use_gisa

The boolean module parameter "kvm.use_gisa" controls if newly
created guests will use the GISA facility if provided by the
host system. The default is yes.

  # cat /sys/module/kvm/parameters/use_gisa
  Y

The parameter can be changed on the fly.

  # echo N > /sys/module/kvm/parameters/use_gisa

Already running guests are not affected by this change.

The kvm s390 debug feature shows if a guest is running with GISA.

  # grep gisa /sys/kernel/debug/s390dbf/kvm-$pid/sprintf
  00 01582725059:843303 3 - 08 00000000e119bc01  gisa 0x00000000c9ac2642 initialized
  00 01582725059:903840 3 - 11 000000004391ee22  00[0000000000000000-0000000000000000]: AIV gisa format-1 enabled for cpu 000
  ...
  00 01582725059:916847 3 - 08 0000000094fff572  gisa 0x00000000c9ac2642 cleared

In general, that value should not be changed as the GISA facility
enhances interruption delivery performance.

A reason to switch the GISA facility off might be a performance
comparison run or debugging.

Signed-off-by: Michael Mueller <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Cornelia Huck <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Signed-off-by: Christian Borntraeger <[email protected]>

0 files changed, 0 insertions, 0 deletions