Re: [PATCH] s390/vfio-ap: fix unregister GISC when KVM is already gone results in OOPS

[Tony Krowiak <akrowiak@linux.ibm.com>]

In trying to recreate this problem in order to get a stack trace, I 
discovered that
it only occurs within a local repository that has several new patches 
applied,
so the problem is not part of the base code and will be fixed via this 
new set
of patches forthcoming.

On 9/18/20 1:02 PM, Tony Krowiak wrote:
> Attempting to unregister Guest Interruption Subclass (GISC) when the
> link between the matrix mdev and KVM has been removed results in the
> following:
>
>     "Kernel panic -not syncing: Fatal exception: panic_on_oops"
>
> This patch fixes this bug by verifying the matrix mdev and KVM are still
> linked prior to unregistering the GISC.
>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
>   drivers/s390/crypto/vfio_ap_ops.c | 14 +++++++++-----
>   1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e0bde8518745..847a88642644 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -119,11 +119,15 @@ static void vfio_ap_wait_for_irqclear(int apqn)
>    */
>   static void vfio_ap_free_aqic_resources(struct vfio_ap_queue *q)
>   {
> -	if (q->saved_isc != VFIO_AP_ISC_INVALID && q->matrix_mdev)
> -		kvm_s390_gisc_unregister(q->matrix_mdev->kvm, q->saved_isc);
> -	if (q->saved_pfn && q->matrix_mdev)
> -		vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev),
> -				 &q->saved_pfn, 1);
> +	if (q->matrix_mdev) {
> +		if (q->saved_isc != VFIO_AP_ISC_INVALID && q->matrix_mdev->kvm)
> +			kvm_s390_gisc_unregister(q->matrix_mdev->kvm,
> +						 q->saved_isc);
> +		if (q->saved_pfn)
> +			vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev),
> +					 &q->saved_pfn, 1);
> +	}
> +
>   	q->saved_pfn = 0;
>   	q->saved_isc = VFIO_AP_ISC_INVALID;
>   }