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SubjectRe: [PATCH v2 2/3] s390/vfio-ap: set status response code to 06 on gisc registration failure
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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;
>> }
>>
>

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