KVM: s390: allow 255 VCPUs when sca entries aren't used

If the SCA entries aren't used by the hardware (no SIGPIF), we
can simply not set the entries, stick to the basic sca and allow more
than 64 VCPUs.

To hinder any other facility from using these entries, let's properly
provoke intercepts by not setting the MCN and keeping the entries
unset.

This effectively allows when running KVM under KVM (vSIE) or under z/VM to
provide more than 64 VCPUs to a guest. Let's limit it to 255 for now, to
not run into problems if the CPU numbers are limited somewhere else.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 9995cab41950..3a4e97f1a9e6 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -20,6 +20,7 @@
 #include <linux/kvm_host.h>
 #include <asm/facility.h>
 #include <asm/processor.h>
+#include <asm/sclp.h>
 
 typedef int (*intercept_handler_t)(struct kvm_vcpu *vcpu);
 
@@ -387,4 +388,13 @@ static inline union ipte_control *kvm_s390_get_ipte_control(struct kvm *kvm)
 
 	return &sca->ipte_control;
 }
+static inline int kvm_s390_use_sca_entries(void)
+{
+	/*
+	 * Without SIGP interpretation, only SRS interpretation (if available)
+	 * might use the entries. By not setting the entries and keeping them
+	 * invalid, hardware will not access them but intercept.
+	 */
+	return sclp.has_sigpif;
+}
 #endif