Re: [Qemu-devel] [PATCH 3/3] s390: Do not pass inofficial IPL type to the guest

[Viktor VM Mihajlovski]

On 05.04.2018 17:11, David Hildenbrand wrote:
> On 05.04.2018 17:07, Viktor Mihajlovski wrote:
>> IPL over a virtio-scsi device requires special handling not
>> available in the real architecture. For this purpose the IPL
>> type 0xFF has been chosen as means of communication between
>> QEMU and the pc-bios. However, a guest OS could be confused
>> by seeing an unknown IPL type.
>>
>> This change sets the IPL parameter type to 0x02 (CCW) to prevent
>> this. Pre-existing Linux has looked up the IPL parameters only in
>> the case of FCP IPL. This means that the behavior should stay
>> the same even if Linux checks for the IPL type unconditionally.
>>
>> Signed-off-by: Viktor Mihajlovski <address@hidden>
>> ---
>>  pc-bios/s390-ccw/bootmap.c |  7 +++++++
>>  pc-bios/s390-ccw/iplb.h    | 15 +++++++++++++--
>>  2 files changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
>> index fc2a9fe..9287b7a 100644
>> --- a/pc-bios/s390-ccw/bootmap.c
>> +++ b/pc-bios/s390-ccw/bootmap.c
>> @@ -70,6 +70,13 @@ static void jump_to_IPL_code(uint64_t address)
>>  {
>>      /* store the subsystem information _after_ the bootmap was loaded */
>>      write_subsystem_identification();
>> +
>> +    /* prevent unknown IPL types in the guest */
>> +    if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) {
>> +        iplb.pbt = S390_IPL_TYPE_CCW;
>> +        set_iplb(&iplb);
>> +    }
> 
> Confused, doesn't this imply that a system reset immediately after this
> instruction will result in something different getting booted?
> 
Not if the other (QEMU) patches of this series are applied. Without
them, the behavior is the same as with an re-ipl (Today's Linux will
always request a CCW re-ipl).
[...]

-- 
Regards,
  Viktor Mihajlovski