[GIT PULL 04/22] KVM: s390: interrupt: Fix single-stepping userspace-emulated instructions

Janosch Frank
2023-08-24T12:46:55Z

From: Ilya Leoshkevich <iii@linux.ibm.com>

Single-stepping a userspace-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 after arranging a KVM_EXIT_S390_SIEIC exit,
kvm_handle_sie_intercept() calls kvm_s390_handle_per_ifetch_icpt(),
which sets KVM_GUESTDBG_EXIT_PENDING. This bit, however, is not
processed immediately, but rather persists until the next ioctl(),
causing a spurious single-step exit.

Fix by clearing this bit in ioctl().

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20230725143857.228626-5-iii@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
arch/s390/kvm/kvm-s390.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 0c6333b108ba..e6511608280c 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5383,6 +5383,7 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
{
struct kvm_vcpu *vcpu = filp->private_data;
void __user *argp = (void __user *)arg;
+ int rc;

switch (ioctl) {
case KVM_S390_IRQ: {
@@ -5390,7 +5391,8 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,

if (copy_from_user(&s390irq, argp, sizeof(s390irq)))
return -EFAULT;
- return kvm_s390_inject_vcpu(vcpu, &s390irq);
+ rc = kvm_s390_inject_vcpu(vcpu, &s390irq);
+ break;
}
case KVM_S390_INTERRUPT: {
struct kvm_s390_interrupt s390int;
@@ -5400,10 +5402,25 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
return -EFAULT;
if (s390int_to_s390irq(&s390int, &s390irq))
return -EINVAL;
- return kvm_s390_inject_vcpu(vcpu, &s390irq);
+ rc = kvm_s390_inject_vcpu(vcpu, &s390irq);
+ break;
}
+ default:
+ rc = -ENOIOCTLCMD;
+ break;
}
- return -ENOIOCTLCMD;
+
+ /*
+ * To simplify single stepping of userspace-emulated instructions,
+ * KVM_EXIT_S390_SIEIC exit sets KVM_GUESTDBG_EXIT_PENDING (see
+ * should_handle_per_ifetch()). However, if userspace emulation injects
+ * an interrupt, it needs to be cleared, so that KVM_EXIT_DEBUG happens
+ * after (and not before) the interrupt delivery.
+ */
+ if (!rc)
+ vcpu->guest_debug &= ~KVM_GUESTDBG_EXIT_PENDING;
+
+ return rc;
}

static int kvm_s390_handle_pv_vcpu_dump(struct kvm_vcpu *vcpu,
--
2.41.0