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

From: Tony Krowiak <akrowiak@linux.ibm.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, jjherne@linux.ibm.com,
	borntraeger@linux.ibm.com, frankja@linux.ibm.com,
	imbrenda@linux.ibm.com, david@redhat.com
Subject: Re: [PATCH v2 2/3] s390/vfio-ap: set status response code to 06 on gisc registration failure
Date: Fri, 27 Oct 2023 13:06:57 -0400	[thread overview]
Message-ID: <1aa17b46-18ce-403d-b511-ee6c8f7142b3@linux.ibm.com> (raw)
In-Reply-To: <20231027160347.05c6cd60.pasic@linux.ibm.com>

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