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

[Christian Borntraeger]

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....