[PATCH v1 1/4] KVM: s390: vsie: Allow non-zarch guests

[Eric Farman <farman@linux.ibm.com>]

Linux/KVM runs in z/Architecture-only mode. Although z/Architecture
is built upon a long history of hardware refinements, any other
CPU mode is not permitted.

Allow a userspace to explicitly enable the use of ESA mode for
nested guests, otherwise usage will be rejected.

Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h | 1 +
 arch/s390/kvm/vsie.c             | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 3039c88daa63..8a4f4a39f7a2 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -656,6 +656,7 @@ struct kvm_arch {
 	int user_stsi;
 	int user_instr0;
 	int user_operexec;
+	int allow_vsie_esamode;
 	struct s390_io_adapter *adapters[MAX_S390_IO_ADAPTERS];
 	wait_queue_head_t ipte_wq;
 	int ipte_lock_count;
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 72895dddc39a..888370a02ef7 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -125,8 +125,9 @@ static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
 	int newflags, cpuflags = atomic_read(&scb_o->cpuflags);
 
-	/* we don't allow ESA/390 guests */
-	if (!(cpuflags & CPUSTAT_ZARCH))
+	newflags = 0;
+	/* we don't allow ESA/390 guests unless explicitly enabled */
+	if (!(cpuflags & CPUSTAT_ZARCH) && !vcpu->kvm->arch.allow_vsie_esamode)
 		return set_validity_icpt(scb_s, 0x0001U);
 
 	if (cpuflags & (CPUSTAT_RRF | CPUSTAT_MCDS))
@@ -135,7 +136,8 @@ static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 		return set_validity_icpt(scb_s, 0x0007U);
 
 	/* intervention requests will be set later */
-	newflags = CPUSTAT_ZARCH;
+	if (cpuflags & CPUSTAT_ZARCH)
+		newflags = CPUSTAT_ZARCH;
 	if (cpuflags & CPUSTAT_GED && test_kvm_facility(vcpu->kvm, 8))
 		newflags |= CPUSTAT_GED;
 	if (cpuflags & CPUSTAT_GED2 && test_kvm_facility(vcpu->kvm, 78)) {
-- 
2.51.0