Re: [PATCH v3 3/6] KVM: s390: interrupt: Fix single-stepping kernel-emulated instructions

Claudio Imbrenda
2023-07-25T13:53:44Z

On Mon, 24 Jul 2023 11:44:09 +0200
Ilya Leoshkevich <iii@linux.ibm.com> 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.
>
> Reviewed-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> 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;
> }