Re: [PATCH v3 4/4] pc-bios/s390x: Fix reset psw mask

[Thomas Huth <thuth@redhat.com>]

On 17/12/2019 13.36, Thomas Huth wrote:
> On 13/12/2019 13.06, Cornelia Huck wrote:
>> On Thu, 5 Dec 2019 11:12:39 +0100
>> Cornelia Huck <cohuck@redhat.com> wrote:
>>
>>> On Tue,  3 Dec 2019 08:28:13 -0500
>>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>>
>>>> We need to set the short psw indication bit in the reset psw, as it is
>>>> a short psw.
>>>>
>>>> fixes: 9629823290 ("pc-bios/s390-ccw: do a subsystem reset before running the guest")
>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>> ---
>>>>  pc-bios/s390-ccw/jump2ipl.c | 12 +++++++-----
>>>>  1 file changed, 7 insertions(+), 5 deletions(-)  
>>>
>>> Thanks, applied (together with a rebuild of the bios images.)
>>
>> This unfortunately breaks 'make check-qtest-s390x':
>>
>>    TEST    check-qtest-s390x: tests/boot-serial-test
>>    TEST    check-qtest-s390x: tests/pxe-test
>> ERROR - too few tests run (expected 1, got 0)
>>
>> When I revert this, the rebuild, and "s390x: Properly fetch and test
>> the short psw on diag308 subc 0/1" (as it exposes the bug this commit
>> tried to fix), everything passes again. No idea what is wrong, though :(
>>
>> For now, I've dropped the three patches mentioned above from the
>> s390-next branch (I plan to send a pull request later). Let's fix this
>> on top once we figured out whatever went wrong, no need to rush here.
> 
> I think I might have found the problem. You now need this patch on top
> to get it working again:
> 
> diff a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
> --- a/pc-bios/s390-ccw/jump2ipl.c
> +++ b/pc-bios/s390-ccw/jump2ipl.c
> @@ -18,7 +18,7 @@
>  typedef struct ResetInfo {
>      uint64_t ipl_psw;
>      uint32_t ipl_continue;
> -} ResetInfo;
> +} __attribute__((packed)) ResetInfo;
> 
>  static ResetInfo save;
> 
> Without this patch, there is now a 32-bit padding in the struct. Not
> sure why it then fails (I had a quick look at the disassembly of
> jump2ipl.o and could not spot anything that was obviously wrong), but if
> I mark the struct as "packed" to get the old size again, then the
> pxe-test is working fine for me again.

Never mind, the problem was not in the jump2ipl.c code, but in the
pxe-test: The code only worked if the r3 register contained only zeroes
in the upper bits. The changes to jump2ipl.c here caused the compiler to
put a different value in r3, so the test suddenly crashed. I've now sent
a patch to fix the test ("tests/boot-sector: Fix the bad s390x assembler
code").

 Thomas