[PATCH 1/2] KVM: s390: interrupt: Fix stepping into interrupt handlers

[Ilya Leoshkevich <iii@xxxxxxxxxxxxx>]

Currently, after single-stepping an instruction that causes a program
interrupt, GDB ends up on the second instruction of the program
interrupt handler.

The reason is that vcpu_pre_run() manually delivers the program
interrupt, and then __vcpu_run() runs the first handler instruction
using the CPUSTAT_P flag. This causes a KVM_SINGLESTEP exit on the
second handler instruction.

Instead, KVM needs to do a KVM_SINGLESTEP exit after the manual
interrupt delivery.

Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
 arch/s390/kvm/interrupt.c | 10 ++++++++++
 arch/s390/kvm/kvm-s390.c  |  4 ++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 9250fde1f97d..e633ec4f98d8 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1392,6 +1392,7 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int;
 	int rc = 0;
+	bool delivered = false;
 	unsigned long irq_type;
 	unsigned long irqs;
 
@@ -1465,6 +1466,15 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu)
 			WARN_ONCE(1, "Unknown pending irq type %ld", irq_type);
 			clear_bit(irq_type, &li->pending_irqs);
 		}
+		delivered |= !rc;
+	}
+
+	if (delivered && guestdbg_sstep_enabled(vcpu)) {
+		struct kvm_debug_exit_arch *debug_exit = &vcpu->run->debug.arch;
+
+		debug_exit->addr = vcpu->arch.sie_block->gpsw.addr;
+		debug_exit->type = KVM_SINGLESTEP;
+		vcpu->guest_debug |= KVM_GUESTDBG_EXIT_PENDING;
 	}
 
 	set_intercept_indicators(vcpu);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 39b36562c043..2d66d83b682c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4607,7 +4607,7 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu)
 
 	if (!kvm_is_ucontrol(vcpu->kvm)) {
 		rc = kvm_s390_deliver_pending_interrupts(vcpu);
-		if (rc)
+		if (rc || guestdbg_exit_pending(vcpu))
 			return rc;
 	}
 
@@ -4734,7 +4734,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 
 	do {
 		rc = vcpu_pre_run(vcpu);
-		if (rc)
+		if (rc || guestdbg_exit_pending(vcpu))
 			break;
 
 		kvm_vcpu_srcu_read_unlock(vcpu);
-- 
2.41.0