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

Ilya Leoshkevich
2023-07-24T09:50:32Z

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>
---
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);
--
2.41.0