Re: [RFC 17/37] DOCUMENTATION: protvirt: Instruction emulation

[Janosch Frank <frankja@linux.ibm.com>]

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On 11/14/19 5:03 PM, Cornelia Huck wrote:
> On Thu, 14 Nov 2019 16:55:46 +0100
> Janosch Frank <frankja@linux.ibm.com> wrote:
> 
>> On 11/14/19 4:41 PM, Cornelia Huck wrote:
>>> On Thu, 14 Nov 2019 16:20:24 +0100
>>> Claudio Imbrenda <imbrenda@linux.ibm.com> wrote:
>>>   
>>>> On Thu, 14 Nov 2019 16:15:26 +0100
>>>> Cornelia Huck <cohuck@redhat.com> wrote:
>>>>  
>>>>> On Thu, 24 Oct 2019 07:40:39 -0400
>>>>> Janosch Frank <frankja@linux.ibm.com> wrote:
> 
>>>>>> +The Secure Instruction Data Area contains instruction storage
>>>>>> +data. Data for diag 500 is exempt from that and has to be moved
>>>>>> +through shared buffers to KVM.      
>>>>>
>>>>> I find this paragraph a bit confusing. What does that imply for diag
>>>>> 500 interception? Data is still present in gprs 1-4?    
>>>>
>>>> no registers are leaked in the registers. registers are always only
>>>> exposed through the state description.  
>>>
>>> So, what is so special about diag 500, then?  
>>
>> That's mostly a confusion on my side.
>> The SIDAD is 4k max, so we can only move IO "management" data over it
>> like ORBs and stuff. My intention was to point out, that the data which
>> is to be transferred (disk contents, etc.) can't go over the SIDAD but
>> needs to be in a shared page.
>>
>> diag500 was mostly a notification mechanism without a lot of data, right?
> 
> Yes; the main information in there are the schid identifying the
> subchannel, the virtqueue number, and a cookie value, all of which fit
> into the registers.
> 
> So this goes via the sidad as well?
> 

Only referenced data goes over the SIDA, register values go into offset
0x380 of the SIE state description.

If an instruction has an address in a register, we will receive a bogus
address and the referenced data in the SIDA.

SCLP has a code and an address as register values.
We will get the code and a bogus address in the register area.
The SCCB will be in the SIDA.


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