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

[Christian Borntraeger]

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?