Commit 1ad1fa82 authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Janosch Frank
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KVM: s390: interrupt: Fix single-stepping userspace-emulated instructions 



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: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20230725143857.228626-5-iii@linux.ibm.com>
Signed-off-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: default avatarJanosch Frank <frankja@linux.ibm.com>
parent ba853a4e

arch/s390/kvm/kvm-s390.c

+20 −3
Original line number Diff line number Diff line
@@ -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,