linux-kernel - Re: [PATCH v2 2/3] s390/vfio-ap: set status response code to 06 on gisc registration failure

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Date:   Fri, 27 Oct 2023 12:56:38 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, jjherne@...ux.ibm.com,
        borntraeger@...ux.ibm.com, frankja@...ux.ibm.com,
        imbrenda@...ux.ibm.com, david@...hat.com,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH v2 2/3] s390/vfio-ap: set status response code to 06 on
 gisc registration failure

On Wed, 18 Oct 2023 09:38:24 -0400
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> From: Anthony Krowiak <akrowiak@...ux.ibm.com>
> 
> The interception handler for the PQAP(AQIC) command calls the
> kvm_s390_gisc_register function to register the guest ISC with the channel
> subsystem. If that call fails, the status response code 08 - indicating
> Invalid ZONE/GISA designation - is returned to the guest. This response
> code does not make sense because the non-zero return code from the
> kvm_s390_gisc_register function can be due one of two things: Either the
> ISC passed as a parameter by the guest to the PQAP(AQIC) command is greater
> than the maximum ISC value allowed, or the guest is not using a GISA.

The "ISC passed as a parameter by the guest to the PQAP(AQIC) command is
greater than the maximum ISC value allowed" is not possible. The isc is
3 bits wide and all 8 values that can be represented on 3 bits are valid.

This is only possible if the hypervisor was to mess up, or if the machine
was broken.

> 
> Since this scenario is very unlikely to happen and there is no status
> response code to indicate an invalid ISC value, let's set the
> response code to 06 indicating 'Invalid address of AP-queue notification
> byte'. While this is not entirely accurate, it is better than indicating
> that the ZONE/GISA designation is invalid which is something the guest
> can do nothing about since those values are set by the hypervisor.
> 
> Signed-off-by: Anthony Krowiak <akrowiak@...ux.ibm.com>
> Suggested-by: Halil Pasic <pasic@...ux.ibm.com>


> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 9cb28978c186..25d7ce2094f8 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -393,8 +393,8 @@ static int ensure_nib_shared(unsigned long addr, struct gmap *gmap)
>   * Register the guest ISC to GIB interface and retrieve the
>   * host ISC to issue the host side PQAP/AQIC
>   *
> - * Response.status may be set to AP_RESPONSE_INVALID_ADDRESS in case the
> - * vfio_pin_pages failed.
> + * status.response_code may be set to AP_RESPONSE_INVALID_ADDRESS in case the
> + * vfio_pin_pages or kvm_s390_gisc_register failed.
>   *
>   * Otherwise return the ap_queue_status returned by the ap_aqic(),
>   * all retry handling will be done by the guest.
> @@ -458,7 +458,7 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
>  				 __func__, nisc, isc, q->apqn);
>  
>  		vfio_unpin_pages(&q->matrix_mdev->vdev, nib, 1);
> -		status.response_code = AP_RESPONSE_INVALID_GISA;
> +		status.response_code = AP_RESPONSE_INVALID_ADDRESS;
>  		return status;
>  	}
>