Re: [PATCH] pc-bios: s390x: Only set lowcore iplb address on list-directed IPL

["Jason J. Herne" <jjherne@linux.ibm.com>]

On 8/17/20 12:30 PM, Cornelia Huck wrote:
> On Mon, 17 Aug 2020 10:17:34 -0400
> "Jason J. Herne" <jjherne@linux.ibm.com> wrote:
> 
>> The POP states that the IPLB location is only written to 0x14 for
>> list-directed IPL. Some operating systems expect 0x14 to not change on
>> boot and will fail IPL if it does change.
>>
>> Fixes: 9bfc04f9ef6802fff0
> 
> Should be
> 
> Fixes: 9bfc04f9ef68 ("pc-bios: s390x: Save iplb location in lowcore")
> 
>> Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
>> Reviewed-by: Janosch Frank <frankja@de.ibm.com>
>> ---
>>   pc-bios/s390-ccw/jump2ipl.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
>> index 767012bf0c..5e3e13f4b0 100644
>> --- a/pc-bios/s390-ccw/jump2ipl.c
>> +++ b/pc-bios/s390-ccw/jump2ipl.c
>> @@ -33,7 +33,10 @@ void jump_to_IPL_code(uint64_t address)
>>   {
>>       /* store the subsystem information _after_ the bootmap was loaded */
>>       write_subsystem_identification();
>> -    write_iplb_location();
>> +
>> +    if (iplb.pbt != S390_IPL_TYPE_CCW) {
>> +            write_iplb_location();
>> +    }
> 
> What happens for ipl types other than CCW and FCP? IOW, should that
> rather be a positive check for S390_IPL_TYPE_FCP?
> 
>>   
>>       /* prevent unknown IPL types in the guest */
>>       if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
> 

Based on my (admittedly limited) understanding of the architecture and
code, I believe write_iplb_location() should be called at least for
S390_IPL_TYPE_FCP but I'm not 100% sure on S390_IPL_TYPE_QEMU_SCSI.
Perhaps Janosch has an idea?

It was originally unconditional, and my new conditional excludes vfio
CCW which is definitely a step in the right direction, in any case :).


-- 
-- Jason J. Herne (jjherne@linux.ibm.com)