Re: [PATCH v3 1/6] KVM: s390: interrupt: Fix single-stepping into interrupt handlers

Claudio Imbrenda
2023-07-25T13:53:47Z

On Mon, 24 Jul 2023 11:44:07 +0200
Ilya Leoshkevich <iii@linux.ibm.com> wrote:

> After single-stepping an instruction that generates an interrupt, GDB
> ends up on the second instruction of the respective interrupt handler.
>
> The reason is that vcpu_pre_run() manually delivers the 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.
>
> Fix by delaying the KVM_SINGLESTEP exit until after the manual
> interrupt delivery.
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>

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

> ---
> arch/s390/kvm/interrupt.c | 14 ++++++++++++++
> arch/s390/kvm/kvm-s390.c | 4 ++--
> 2 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 9bd0a873f3b1..85e39f472bb4 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 +1466,19 @@ 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;
> + }
> +
> + /*
> + * We delivered at least one interrupt and modified the PC. Force a
> + * singlestep event now.
> + */
> + 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 d1e768bcfe1d..0c6333b108ba 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4611,7 +4611,7 @@ 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;
> }
>
> @@ -4738,7 +4738,7 @@ 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);