Re: [PATCH v2 3/6] KVM: s390: interrupt: Fix single-stepping kernel-emulated instructions

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On 21.07.23 13:57, Ilya Leoshkevich wrote:
Single-stepping a kernel-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 kvm_handle_sie_intercept(), after injecting the
interrupt, also processes the PER event and arranges a KVM_SINGLESTEP
exit. The interrupt is not yet delivered, however, so the userspace
sees the next instruction.

Fix by avoiding the KVM_SINGLESTEP exit when there is a pending
interrupt. The next __vcpu_run() loop iteration will arrange a
KVM_SINGLESTEP exit after delivering the interrupt.

Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
  arch/s390/kvm/intercept.c | 17 ++++++++++++++---
  1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 7cdd927541b0..d2f7940c5d03 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -583,6 +583,19 @@ static int handle_pv_notification(struct kvm_vcpu *vcpu)
  	return handle_instruction(vcpu);
  }
+static bool should_handle_per_ifetch(const struct kvm_vcpu *vcpu, int rc)
+{
+	/* Process PER, also if the instruction is processed in user space. */
+	if (!(vcpu->arch.sie_block->icptstatus & 0x02))
+		return false;
+	if (rc != 0 && rc != -EOPNOTSUPP)
+		return false;
+	if (guestdbg_sstep_enabled(vcpu) && vcpu->arch.local_int.pending_irqs)
+		/* __vcpu_run() will exit after delivering the interrupt. */
+		return false;
+	return true;
+}
+
  int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
  {
  	int rc, per_rc = 0;
@@ -645,9 +658,7 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
  		return -EOPNOTSUPP;
  	}
- /* process PER, also if the instruction is processed in user space */
-	if (vcpu->arch.sie_block->icptstatus & 0x02 &&
-	    (!rc || rc == -EOPNOTSUPP))
+	if (should_handle_per_ifetch(vcpu, rc))
  		per_rc = kvm_s390_handle_per_ifetch_icpt(vcpu);
  	return per_rc ? per_rc : rc;
  }

Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb




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