KVM: s390: Support keyless subset guest mode

If the KSS facility is available on the machine, we also make it
available for our KVM guests.

The KSS facility bypasses storage key management as long as the guest
does not issue a related instruction. When that happens, the control is
returned to the host, which has to turn off KSS for a guest vcpu
before retrying the instruction.

Signed-off-by: Corey S. McQuay <csmcquay@linux.vnet.ibm.com>
Signed-off-by: Farhan Ali <alifm@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

5 files changed, 29 insertions, 8 deletions

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index f5378f3..a4752bf 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -426,6 +426,9 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
 	case ICPT_PARTEXEC:
 		rc = handle_partial_execution(vcpu);
 		break;
+	case ICPT_KSS:
+		rc = kvm_s390_skey_check_enable(vcpu);
+		break;
 	default:
 		return -EOPNOTSUPP;
 	}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 11b7d66..8771fef 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -300,6 +300,8 @@ static void kvm_s390_cpu_feat_init(void)
 		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_CEI);
 	if (sclp.has_ibs)
 		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_IBS);
+	if (sclp.has_kss)
+		allow_cpu_feat(KVM_S390_VM_CPU_FEAT_KSS);
 	/*
 	 * KVM_S390_VM_CPU_FEAT_SKEY: Wrong shadow of PTE.I bits will make
 	 * all skey handling functions read/set the skey from the PGSTE
@@ -2034,7 +2036,11 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 	vcpu->arch.sie_block->sdnxo = ((unsigned long) &vcpu->run->s.regs.sdnx)
 					| SDNXC;
 	vcpu->arch.sie_block->riccbd = (unsigned long) &vcpu->run->s.regs.riccb;
-	vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
+
+	if (sclp.has_kss)
+		atomic_or(CPUSTAT_KSS, &vcpu->arch.sie_block->cpuflags);
+	else
+		vcpu->arch.sie_block->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
 
 	if (vcpu->kvm->arch.use_cmma) {
 		rc = kvm_s390_vcpu_setup_cmma(vcpu);
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index 455124f..55f5c84 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -254,6 +254,7 @@ int kvm_s390_handle_lpsw(struct kvm_vcpu *vcpu);
 int kvm_s390_handle_stctl(struct kvm_vcpu *vcpu);
 int kvm_s390_handle_lctl(struct kvm_vcpu *vcpu);
 int kvm_s390_handle_eb(struct kvm_vcpu *vcpu);
+int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu);
 
 /* implemented in vsie.c */
 int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu);
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index 0ffe973..c03106c 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -198,18 +198,25 @@ static int handle_store_cpu_address(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
-static int __skey_check_enable(struct kvm_vcpu *vcpu)
+int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
 {
 	int rc = 0;
+	struct kvm_s390_sie_block *sie_block = vcpu->arch.sie_block;
 
 	trace_kvm_s390_skey_related_inst(vcpu);
-	if (!(vcpu->arch.sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)))
+	if (!(sie_block->ictl & (ICTL_ISKE | ICTL_SSKE | ICTL_RRBE)) &&
+	    !(atomic_read(&sie_block->cpuflags) & CPUSTAT_KSS))
 		return rc;
 
 	rc = s390_enable_skey();
 	VCPU_EVENT(vcpu, 3, "enabling storage keys for guest: %d", rc);
-	if (!rc)
-		vcpu->arch.sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE | ICTL_RRBE);
+	if (!rc) {
+		if (atomic_read(&sie_block->cpuflags) & CPUSTAT_KSS)
+			atomic_andnot(CPUSTAT_KSS, &sie_block->cpuflags);
+		else
+			sie_block->ictl &= ~(ICTL_ISKE | ICTL_SSKE |
+					     ICTL_RRBE);
+	}
 	return rc;
 }
 
@@ -218,7 +225,7 @@ static int try_handle_skey(struct kvm_vcpu *vcpu)
 	int rc;
 
 	vcpu->stat.instruction_storage_key++;
-	rc = __skey_check_enable(vcpu);
+	rc = kvm_s390_skey_check_enable(vcpu);
 	if (rc)
 		return rc;
 	if (sclp.has_skey) {
@@ -916,7 +923,7 @@ static int handle_pfmf(struct kvm_vcpu *vcpu)
 		}
 
 		if (vcpu->run->s.regs.gprs[reg1] & PFMF_SK) {
-			int rc = __skey_check_enable(vcpu);
+			int rc = kvm_s390_skey_check_enable(vcpu);
 
 			if (rc)
 				return rc;
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 025b1f2..4719ecb 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -117,6 +117,8 @@ static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 		newflags |= cpuflags & CPUSTAT_SM;
 	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_IBS))
 		newflags |= cpuflags & CPUSTAT_IBS;
+	if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_KSS))
+		newflags |= cpuflags & CPUSTAT_KSS;
 
 	atomic_set(&scb_s->cpuflags, newflags);
 	return 0;
@@ -289,7 +291,9 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	 * bits. Therefore we cannot provide interpretation and would later
 	 * have to provide own emulation handlers.
 	 */
-	scb_s->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
+	if (!(atomic_read(&scb_s->cpuflags) & CPUSTAT_KSS))
+		scb_s->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE;
+
 	scb_s->icpua = scb_o->icpua;
 
 	if (!(atomic_read(&scb_s->cpuflags) & CPUSTAT_SM))