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authorMichael Mueller <mimu@linux.ibm.com>2020-02-27 10:10:31 +0100
committerChristian Borntraeger <borntraeger@de.ibm.com>2020-02-27 19:47:13 +0100
commitcc674ef252f4750bdcea1560ff491081bb960954 (patch)
tree8f1735b69f2dd1b8fbd4d535ca5b00b50db8a309 /arch/s390
parent04ed89dc4aeba57ab99df16edbd9d06e43d0a2c4 (diff)
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 <mimu@linux.ibm.com> Link: https://lore.kernel.org/r/20200227091031.102993-1-mimu@linux.ibm.com Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Diffstat (limited to 'arch/s390')
-rw-r--r--arch/s390/kvm/kvm-s390.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index f4cd436ba979..6b1842a9feed 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -185,6 +185,11 @@ static u8 halt_poll_max_steal = 10;
module_param(halt_poll_max_steal, byte, 0644);
MODULE_PARM_DESC(halt_poll_max_steal, "Maximum percentage of steal time to allow polling");
+/* if set to true, the GISA will be initialized and used if available */
+static bool use_gisa = true;
+module_param(use_gisa, bool, 0644);
+MODULE_PARM_DESC(use_gisa, "Use the GISA if the host supports it.");
+
/*
* For now we handle at most 16 double words as this is what the s390 base
* kernel handles and stores in the prefix page. If we ever need to go beyond
@@ -2732,7 +2737,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
kvm->arch.use_skf = sclp.has_skey;
spin_lock_init(&kvm->arch.start_stop_lock);
kvm_s390_vsie_init(kvm);
- kvm_s390_gisa_init(kvm);
+ if (use_gisa)
+ kvm_s390_gisa_init(kvm);
KVM_EVENT(3, "vm 0x%pK created by pid %u", kvm, current->pid);
return 0;