Re: [PATCH 7/7] pc-bios: s390x: Setup io and ext new psws only once

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 15.07.20 15:13, Janosch Frank wrote:
> On 7/15/20 11:40 AM, Janosch Frank wrote:
>> Absolutely no need to set them up every time before we enable our
>> interrupt masks.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> 
> So, this one doesn't seem to be a great idea as a kernel loaded to 0x0
> will overwrite the ext/io new PSWs and we'll then try to load a zero PSW
> when an IRQ hits.
> 
> We have two options:
> * Add a piece of code that fixes the low core after a kernel has been loaded
> * Leave the code as is and add a comment, so other people don't fall
> into this trap.
> 
> I'd be fine with both and for now I'd settle for the second option.

Yes, leave it as is and add a comment. 
> 
>> ---
>>  pc-bios/s390-ccw/start.S | 30 +++++++++++++-----------------
>>  1 file changed, 13 insertions(+), 17 deletions(-)
>>
>> diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
>> index 01c4c21b26..0059a15d21 100644
>> --- a/pc-bios/s390-ccw/start.S
>> +++ b/pc-bios/s390-ccw/start.S
>> @@ -34,6 +34,12 @@ loop:
>>  remainder:
>>  	larl	%r2,memsetxc
>>  	ex	%r3,0(%r2)
>> +        /* Store io new PSW */
>> +        larl	%r1,io_new_psw
>> +        mvc	0x1f0(16),0(%r1)
>> +	/* Store ext new PSW */
>> +        larl	%r1,external_new_psw
>> +        mvc	0x1b0(16),0(%r1)
>>  done:
>>  	j      main		/* And call C */
>>  
>> @@ -64,11 +70,6 @@ consume_sclp_int:
>>          stctg   %c0,%c0,0(%r15)
>>          oi      6(%r15),0x2
>>          lctlg   %c0,%c0,0(%r15)
>> -        /* prepare external call handler */
>> -        larl %r1, external_new_code
>> -        stg %r1, 0x1b8
>> -        larl %r1, external_new_mask
>> -        mvc 0x1b0(8),0(%r1)
>>          /* load enabled wait PSW */
>>          larl %r1, enabled_wait_psw
>>          lpswe 0(%r1)
>> @@ -81,14 +82,9 @@ consume_sclp_int:
>>          .globl consume_io_int
>>  consume_io_int:
>>          /* enable I/O interrupts in cr6 */
>> -        stctg %c6,%c6,0(%r15)
>> -        oi    4(%r15), 0xff
>> -        lctlg %c6,%c6,0(%r15)
>> -        /* prepare i/o call handler */
>> -        larl  %r1, io_new_code
>> -        stg   %r1, 0x1f8
>> -        larl  %r1, io_new_mask
>> -        mvc   0x1f0(8),0(%r1)
>> +        stctg	%c6, %c6, 0(%r15)
>> +        oi	4(%r15), 0xff
>> +        lctlg	%c6, %c6, 0(%r15)
>>          /* load enabled wait PSW */
>>          larl  %r1, enabled_wait_psw
>>          lpswe 0(%r1)
>> @@ -112,7 +108,7 @@ disabled_wait_psw:
>>          .quad   PSW_MASK_DWAIT, 0x0000000000000000
>>  enabled_wait_psw:
>>          .quad   PSW_MASK_EWAIT, 0x0000000000000000
>> -external_new_mask:
>> -        .quad   PSW_MASK_64
>> -io_new_mask:
>> -        .quad   PSW_MASK_64
>> +external_new_psw:
>> +        .quad   PSW_MASK_64, external_new_code
>> +io_new_psw:
>> +        .quad   PSW_MASK_64, io_new_code
>>
> 
>