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

Message ID 20230721120046.2262291-4-iii@linux.ibm.com
State New
Headers
Series KVM: s390: interrupt: Fix stepping into interrupt handlers |

Commit Message

Ilya Leoshkevich July 21, 2023, 11:57 a.m. UTC 
  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@linux.ibm.com>
---
 arch/s390/kvm/intercept.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

Comments

David Hildenbrand July 24, 2023, 8:27 a.m. UTC | #1 
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@linux.ibm.com>
> ---
>   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@redhat.com>
diff mbox series

Patch

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;
 }