Re: [PATCH v2 06/13] s390x: protvirt: KVM intercept changes

[Janosch Frank]

On 12/6/19 9:29 AM, Cornelia Huck wrote:
> On Fri, 6 Dec 2019 08:44:52 +0100
> Janosch Frank <address@hidden> wrote:
> 
>> On 12/5/19 6:46 PM, Cornelia Huck wrote:
>>> On Thu, 5 Dec 2019 18:34:32 +0100
>>> Janosch Frank <address@hidden> wrote:
>>>   
>>>> On 12/5/19 6:15 PM, Cornelia Huck wrote:  
>>>>> On Fri, 29 Nov 2019 04:48:02 -0500
>>>>> Janosch Frank <address@hidden> wrote:
>>>>>     
>>>>>> Secure guests no longer intercept with code 4 for an instruction
>>>>>> interception. Instead they have codes 104 and 108 for secure
>>>>>> instruction interception and secure instruction notification
>>>>>> respectively.
>>>>>>
>>>>>> The 104 mirrors the 4 interception.
>>>>>>
>>>>>> The 108 is a notification interception to let KVM and QEMU know that
>>>>>> something changed and we need to update tracking information or
>>>>>> perform specific tasks. It's currently taken for the following
>>>>>> instructions:
>>>>>>
>>>>>> * stpx (To inform about the changed prefix location)
>>>>>> * sclp (On incorrect SCCB values, so we can inject a IRQ)
>>>>>> * sigp (All but "stop and store status")
>>>>>> * diag308 (Subcodes 0/1)
>>>>>>
>>>>>> Signed-off-by: Janosch Frank <address@hidden>
>>>>>> ---
>>>>>>  target/s390x/kvm.c | 6 ++++++
>>>>>>  1 file changed, 6 insertions(+)
>>>>>>  
>>>   
>>>>>> @@ -1664,6 +1668,8 @@ static int handle_intercept(S390CPU *cpu)
>>>>>>              (long)cs->kvm_run->psw_addr);
>>>>>>      switch (icpt_code) {
>>>>>>          case ICPT_INSTRUCTION:
>>>>>> +        case ICPT_PV_INSTR:
>>>>>> +        case ICPT_PV_INSTR_NOTIFICATION:
>>>>>>              r = handle_instruction(cpu, run);    
>>>>>
>>>>> I'm still a bit uneasy about going through the same path for both 104
>>>>> and 108. How does the handler figure out whether it should emulate an
>>>>> instruction, or just process a notification? Is it guaranteed that a
>>>>> given instruction is always showing up as either a 104 or a 108, so
>>>>> that the handler can check the pv state?    
>>>>
>>>> diag 308 subcode 0/1 are 108, but all other subcodes are defined as a
>>>> 104 (if they are an exit at all)...  
>>>
>>> I think that's a reason to really split 108 from 4/104, or at least add
>>> an parameter...  
>>
>> And still call the diag 308 handler or have separate handlers?
> 
> I'd probably split it into a "normal" one and one for pv special
> handling... does that make sense?
> 
IMHO: not really
We still need to do ipa/ipb parsing for both paths, which will result in
code duplication. Looking at diag308 subcode 4, we would have a code 4
one which just does the device resets and reboots and one which does all
that, plus the teardown of the protected guest.

I tried to inline as much as possible to have as little changes as
possible. Notable exception is sclp, which has more checks than
emulation code...

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