Re: [Qemu-devel] [PATCH v3 2/3] pc-bios/s390-ccw/net: Use diag308 to reset machine before jumping to the OS

[Thomas Huth]

On 25.04.2018 18:03, Christian Borntraeger wrote:
> 
> 
> On 04/25/2018 05:36 PM, Thomas Huth wrote:
>> On 25.04.2018 14:44, Christian Borntraeger wrote:
>>>
>>>
>>> On 04/25/2018 02:41 PM, Christian Borntraeger wrote:
>>>> You load from address 0. 
>>>>
>>>> On 04/25/2018 02:34 PM, Thomas Huth wrote:
>>>>> On 25.04.2018 14:18, Christian Borntraeger wrote:
>>>>>>
>>>>>> On 04/25/2018 11:08 AM, Thomas Huth wrote:
>>>>>>
>>>>>>> --- a/pc-bios/s390-ccw/netmain.c
>>>>>>> +++ b/pc-bios/s390-ccw/netmain.c
>>>>>>> @@ -283,6 +283,15 @@ void panic(const char *string)
>>>>>>>      }
>>>>>>>  }
>>>>>>>  
>>>>>>> +void write_subsystem_identification(void)
>>>>>>> +{
>>>>>>> +    uint32_t *schid = (uint32_t *) 184;
>>>>>>> +    uint32_t *zeroes = (uint32_t *) 188;
>>>>>>> +
>>>>>>> +    *schid = 0;         /* We must not set this for virtio-net */
>>>>>>> +    *zeroes = 0;
>>>>>>> +}
>>>>>>> +
>>>>>>
>>>>>> I think we actually want to have the CCW devno of that network device
>>>>>> stored. It has some value to know which CCW device we bootet from, no?
>>>>>
>>>>> Actually, I tried that first (and it took quite some time to debug it),
>>>>> but the Linux kernel then bails out quite early, without any error
>>>>> message. The trace looks like this:
>>>>>
>>>>> 0x0000000007801802:  diag %r1,%r1,776
>>>>> 0x0000000007801780:  larl %r2,0x7831004
>>>>> 0x0000000007801786:  llgf %r1,8
>>>>> 0x000000000780178c:  mvc  0(12,%r0),0(%r2)
>>>>> 0x0000000007801792:  br   %r1
>>>>> 0x0000000000000418:  bas  %r14,512
>>>>> 0x0000000000000200:  mvi  163,1
>>>>> 0x0000000000000204:  slr  %r0,%r0
>>>>> 0x0000000000000206:  lhi  %r1,2
>>>>> 0x000000000000020a:  sigp %r1,%r0,18
>>>>> 0x000000000000020e:  bras %r13,0x252
>>>>> 0x0000000000000252:  lmh  %r0,%r15,0(%r13)
>>>>> 0x0000000000000258:  sam31
>>>>> 0x000000000000025a:  br   %r14
>>>>> 0x000000000000041c:  lh   %r1,184
>>>>> 0x0000000000000420:  bct  %r1,1322
>>>>> 0x0000000000000424:  l    %r1,184
>>>>> 0x0000000000000428:  la   %r2,1840
>>>>> 0x000000000000042c:  bas  %r14,640
>>>>> 0x0000000000000280:  la   %r4,0(%r14)
>>>>> 0x0000000000000284:  la   %r3,792
>>>>> 0x0000000000000288:  la   %r5,804
>>>>> 0x000000000000028c:  la   %r6,888
>>>>> 0x0000000000000290:  la   %r7,20
>>>>> 0x0000000000000294:  st   %r2,4(%r6)
>>>>> 0x0000000000000298:  la   %r2,80(%r2)
>>>>> 0x000000000000029c:  la   %r6,8(%r6)
>>>>> 0x00000000000002a0:  bct  %r7,660
>>>>> 0x00000000000002a4:  lctl %c6,%c6,868
>>>>> 0x00000000000002a8:  slr  %r2,%r2
>>>>> 0x00000000000002aa:  ssch 0(%r3)
>>>>> 0x00000000000002ae:  bne  786
>>>>> 0x0000000000000312:  lpsw 880
>>>>> Guest crashed on cpu 0: disabled-wait
>>>>> PSW: 0x000a000000000000 0x0000000000000000
>>>>>
>>>>> That's the Lloader function in arch/s390/kernel/head.S which is failing
>>>>> here, so seems like Linux tries to load from a block device in case
>>>>> there is a value in 184. Thus I assume that 184 has to contain 0 in this
>>>>> case.
>>>>
>>>> Hmm, I think this is because we jump to 418 for your kernel (which is the 
>>>> loader
>>>> that tries to bootstrap the ccw ipl). When you look at ipl.c we override 
>>>> that
>>>> and jump to 0x10000 instead for linux (which is also hackish) for image 
>>>> files.
>>>> So I guess if we would do a psw restart instead (like you do) on a kernel 
>>>> image
>>>> the normal ipl would also fail....
>>>
>>> FWIW, zipl also loads linux kernels from 0x10000
>>
>> OK, I just checked, and indeed, if I change to code to jump to 0x10000,
>> it also works when setting a value into 184. So I'll change this patch
>> here accordingly.
> 
> This will of course break loading non-Linux binaries.
> Could we maybe check 0x10008 for S390EP (see head.S) which indicates Linux 
> since 3.2 or so
> and only in that case change the address to 0x10000?

Sounds like a good idea! I assume load_iso_bc_entry() in bootmap.c
should use that mechanism, too? And what about hw/s390/ipl.c, should we
change the code there, too?

 Thomas