[PATCH v2 4/6] KVM: s390: interrupt: Fix single-stepping userspace-emulated instructions

[Ilya Leoshkevich]

Single-stepping a userspace-emulated instruction that generates an
interrupt causes GDB to land on the instruction following it instead of
the respective interrupt handler.

The reason is that after arranging a KVM_EXIT_S390_SIEIC exit,
kvm_handle_sie_intercept() calls kvm_s390_handle_per_ifetch_icpt(),
which sets KVM_GUESTDBG_EXIT_PENDING. This bit, however, is not
processed immediately, but rather persists until the next ioctl(),
causing a spurious single-step exit.

Fix by clearing this bit before KVM_EXIT_S390_SIEIC.

Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
 arch/s390/kvm/kvm-s390.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 0c6333b108ba..b717fb8cffed 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5383,6 +5383,7 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
 {
 	struct kvm_vcpu *vcpu = filp->private_data;
 	void __user *argp = (void __user *)arg;
+	int rc;
 
 	switch (ioctl) {
 	case KVM_S390_IRQ: {
@@ -5390,7 +5391,8 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
 
 		if (copy_from_user(&s390irq, argp, sizeof(s390irq)))
 			return -EFAULT;
-		return kvm_s390_inject_vcpu(vcpu, &s390irq);
+		rc = kvm_s390_inject_vcpu(vcpu, &s390irq);
+		break;
 	}
 	case KVM_S390_INTERRUPT: {
 		struct kvm_s390_interrupt s390int;
@@ -5400,10 +5402,18 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
 			return -EFAULT;
 		if (s390int_to_s390irq(&s390int, &s390irq))
 			return -EINVAL;
-		return kvm_s390_inject_vcpu(vcpu, &s390irq);
+		rc = kvm_s390_inject_vcpu(vcpu, &s390irq);
+		break;
 	}
+	default:
+		rc = -ENOIOCTLCMD;
+		break;
 	}
-	return -ENOIOCTLCMD;
+
+	if (!rc)
+		vcpu->guest_debug &= ~KVM_GUESTDBG_EXIT_PENDING;
+
+	return rc;
 }
 
 static int kvm_s390_handle_pv_vcpu_dump(struct kvm_vcpu *vcpu,
-- 
2.41.0