Re: [PATCH 3/7] pc-bios: s390x: Remove unneeded dasd-ipl.c reset psw mask changes

[Janosch Frank]

On 7/20/20 1:45 PM, Thomas Huth wrote:
> On 15/07/2020 11.40, Janosch Frank wrote:
>> jump_to_low_kernel() and the functions that it calls will already or
>> 64 bit addressing into the reset psw mask when executing
>> jump_to_IPL_2() after the diag308 subcode 1.
> 
> But there is also a check in jump_to_low_kernel that could be affected
> by your change:
> 
>     if (*((uint64_t *)0) & RESET_PSW_MASK) {
>         jump_to_IPL_code((*((uint64_t *)0)) & PSW_MASK_SHORT_ADDR);
>     }
> 
> ... but I assume that there should not be any kernels out there in the
> wild which do not have these bits set, so I think your modifications
> here should be ok.

The mask needs to have the short bit indication set so it needs to be !=
0 anyway, no?

> 
> Acked-by: Thomas Huth <thuth@redhat.com>
> 
> 
>> The kernel proper is then branched to rather than doing a full PSW
>> change.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>  pc-bios/s390-ccw/dasd-ipl.c | 3 ---
>>  1 file changed, 3 deletions(-)
>>
>> diff --git a/pc-bios/s390-ccw/dasd-ipl.c b/pc-bios/s390-ccw/dasd-ipl.c
>> index 0fc879bb8e..e8f2846740 100644
>> --- a/pc-bios/s390-ccw/dasd-ipl.c
>> +++ b/pc-bios/s390-ccw/dasd-ipl.c
>> @@ -206,7 +206,6 @@ static void run_ipl2(SubChannelId schid, uint16_t 
>> cutype, uint32_t addr)
>>   */
>>  void dasd_ipl(SubChannelId schid, uint16_t cutype)
>>  {
>> -    PSWLegacy *pswl = (PSWLegacy *) 0x00;
>>      uint32_t ipl2_addr;
>>  
>>      /* Construct Read IPL CCW and run it to read IPL1 from boot disk */
>> @@ -229,7 +228,5 @@ void dasd_ipl(SubChannelId schid, uint16_t cutype)
>>      run_ipl2(schid, cutype, ipl2_addr);
>>  
>>      /* Transfer control to the guest operating system */
>> -    pswl->mask |= PSW_MASK_EAMODE;   /* Force z-mode */
>> -    pswl->addr |= PSW_MASK_BAMODE;   /* ...          */
>>      jump_to_low_kernel();
>>  }
>

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