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

  From: Anthony Krowiak <akrowiak@linux.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.

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@linux.ibm.com>
Suggested-by: Halil Pasic <pasic@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
  

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

> From: Anthony Krowiak <akrowiak@linux.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@linux.ibm.com>
> Suggested-by: Halil Pasic <pasic@linux.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;
>  	}
>
  

On 10/27/23 06:56, Halil Pasic wrote:
> On Wed, 18 Oct 2023 09:38:24 -0400
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> 
>> From: Anthony Krowiak <akrowiak@linux.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.

kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
{
	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;

	if (!gi->origin)
		return -ENODEV;
	if (gisc > MAX_ISC)
		return -ERANGE;
...

Just quoting what is in the code.
> 
>>
>> 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@linux.ibm.com>
>> Suggested-by: Halil Pasic <pasic@linux.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;
>>   	}
>>   
>
  

On Fri, 27 Oct 2023 09:36:26 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> >> 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.  
> 
> kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
> {
> 	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
> 
> 	if (!gi->origin)
> 		return -ENODEV;
> 	if (gisc > MAX_ISC)
> 		return -ERANGE;
> ...
> 
> Just quoting what is in the code.

Right! But it is not the guest that calls this function directly. This
function is called by the vfio_ap code.

The guest passes ISC in bits 61, 62 and 63 of GR1.

So the guest can't give you an invalid value.

Regards,
Halil
  

On 10/27/23 10:03, Halil Pasic wrote:
> On Fri, 27 Oct 2023 09:36:26 -0400
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> 
>>>> 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.
>>
>> kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
>> {
>> 	struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
>>
>> 	if (!gi->origin)
>> 		return -ENODEV;
>> 	if (gisc > MAX_ISC)
>> 		return -ERANGE;
>> ...
>>
>> Just quoting what is in the code.
> 
> Right! But it is not the guest that calls this function directly. This
> function is called by the vfio_ap code.
> 
> The guest passes ISC in bits 61, 62 and 63 of GR1.
> 
> So the guest can't give you an invalid value.

Yes, I got it the first time you said that.

> 
> Regards,
> Halil