Re: [Qemu-devel] [PATCH 4/9] s390x: refactor error handling for SSCH and RSCH

[Halil Pasic <pasic@linux.vnet.ibm.com>]

On 09/25/2017 09:31 AM, Dong Jia Shi wrote:
> * Cornelia Huck <cohuck@redhat.com> [2017-09-08 11:59:50 +0200]:
> 
>> On Fri, 8 Sep 2017 11:21:57 +0200
>> Halil Pasic <pasic@linux.vnet.ibm.com> wrote:
>>
>>> On 09/08/2017 05:41 AM, Dong Jia Shi wrote:
>>>> Let' me summarize here, in case I misunderstand things. Now we have
>>>> two ways to choose:
>>>>
>>>> A. Kernel: no change.
>>>>    Qemu  : handle -EFAULT as option 2 by generating a program check.
>>>>
>>>> B. Kernel: return -EFAULT
>>>>            +
>>>>            update the IRB area in the I/O region for option 1 to present
>>>>            a unit check SCSW (with proper sense byte ECW), and for option
>>>>            2 to present a program check.
>>>>    Qemu  : handle -EFAULT according to the information that the IRB area
>>>>            provided.  
>>>
>>> This is not what I was trying to say. You got my message regarding A, but
>>> B was supposed to be understood like this.
>>>
>>> Keep the current handling for option 1, that is return -EFAULT. For option
>>> 2 do what the spec says, execute the program until the bad address and then
>>> generate a program-check (SCSW) once the bad stuff has it's turn. Thus
>>> the only change in QEMU would be handling -EFAULT with an unit check (because
>>> now it's just option 1).
> Let me adding some context information here by copying some words from the
> previous mail in this thread:
> The only option 2 case in the kernel is ccwchain_fetch_idal() finding a
> bad idaw_iova.
> 
> What you propose to do for this case is (correct me if I get it wrong):
> In ccwchain_fetch_idal(), we do not return -EFAULT, instead we return 0,
> and issuing the incompletely translated channel program with the bad
> address to the physical device. And QEMU will eventually get the SCSW
> with the program-check from the physical device I/O result, and inject
> it to guest for further handling.
> 

I guess that would be the cleanest. I would also be fine with not making
the physical device program-check (issuing a shortened channel program,
and doing the program check in software) but that's probably more
complicated to implement.

> Is this understanding right? If so, I'm fine with that, and I can
> provide the fix in the kernel.
> 

That would be nice.

>>
>> That makes sense to me.
>>
>