KVM: s390: Beautify skey enable check

Let's introduce an explicit check if skeys have already been enabled
for the vcpu, so we don't have to check the mm context if we don't have
the storage key facility.

This lets us check for enablement without having to take the mm
semaphore and thus speedup skey emulation.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Farhan Ali <alifm@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/include/asm/kvm_host.h

@@ -656,6 +656,7 @@ struct kvm_vcpu_arch {
 	seqcount_t cputm_seqcount;
 	__u64 cputm_start;
 	bool gs_enabled;
+	bool skey_enabled;
 };
 
 struct kvm_vm_stat {

arch/s390/kvm/priv.c

@@ -205,13 +205,10 @@ static int handle_store_cpu_address(struct kvm_vcpu *vcpu)
 int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
 {
 	int rc;
-	struct kvm_s390_sie_block *sie_block = vcpu->arch.sie_block;
 
 	trace_kvm_s390_skey_related_inst(vcpu);
 	/* Already enabled? */
-	if (vcpu->kvm->arch.use_skf &&
-	    !(sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)) &&
-	    !kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
+	if (vcpu->arch.skey_enabled)
 		return 0;
 
 	rc = s390_enable_skey();
@@ -222,9 +219,10 @@ int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
 	if (kvm_s390_test_cpuflags(vcpu, CPUSTAT_KSS))
 		kvm_s390_clear_cpuflags(vcpu, CPUSTAT_KSS);
 	if (!vcpu->kvm->arch.use_skf)
-		sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
+		vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
 	else
-		sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
+		vcpu->arch.sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
+	vcpu->arch.skey_enabled = true;
 	return 0;
 }