[PATCH 2/2] KVM: s390: interrupt: Fix stepping into program interrupt handlers

Ilya Leoshkevich
2023-06-29T08:41:26Z

Currently, after single-stepping an instruction that causes a
specification exception, GDB ends up on the instruction immediately
following it.

The reason is that vcpu_post_run() injects the interrupt and sets
KVM_GUESTDBG_EXIT_PENDING, causing a KVM_SINGLESTEP exit. The
interrupt is not delivered, however, therefore userspace sees the
address of the next instruction.

Fix by letting the __vcpu_run() loop go into the next iteration,
where vcpu_pre_run() delivers the interrupt and sets
KVM_GUESTDBG_EXIT_PENDING.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
arch/s390/kvm/intercept.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index 0ee02dae14b2..f8adb64ebda1 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -226,7 +226,22 @@ static int handle_itdb(struct kvm_vcpu *vcpu)
return 0;
}

-#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
+static bool should_handle_per_event(struct kvm_vcpu *vcpu)
+{
+ if (!guestdbg_enabled(vcpu))
+ return false;
+ if (!(vcpu->arch.sie_block->iprcc & PGM_PER))
+ return false;
+ if (guestdbg_sstep_enabled(vcpu) &&
+ vcpu->arch.sie_block->iprcc != PGM_PER) {
+ /*
+ * __vcpu_run() will exit after delivering the concurrently
+ * indicated condition.
+ */
+ return false;
+ }
+ return true;
+}

static int handle_prog(struct kvm_vcpu *vcpu)
{
@@ -242,7 +257,7 @@ static int handle_prog(struct kvm_vcpu *vcpu)
if (kvm_s390_pv_cpu_is_protected(vcpu))
return -EOPNOTSUPP;

- if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
+ if (should_handle_per_event(vcpu)) {
rc = kvm_s390_handle_per_event(vcpu);
if (rc)
return rc;
--
2.41.0