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KVM: s390: interrupt: Fix single-stepping userspace-emulated instructions

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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>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Ilya Leoshkevich 2023-07-25 16:37:19 +02:00 committed by Janosch Frank
parent ba853a4e1c
commit 1ad1fa820e
1 changed files with 20 additions and 3 deletions
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23
arch/s390/kvm/kvm-s390.c
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@ -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,