Re: [PATCH v3 4/5] pc-bios: s390x: Save io and external new PSWs before overwriting them

[Janosch Frank]

On 9/1/20 7:22 PM, Thomas Huth wrote:
> On 31/08/2020 17.09, Janosch Frank wrote:
>> Currently we always overwrite the mentioned exception new PSWs before
>> loading the enabled wait PSW. Let's save the PSW before overwriting
>> and restore it right before starting the loaded kernel.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>  pc-bios/s390-ccw/jump2ipl.c |  4 +++
>>  pc-bios/s390-ccw/netmain.c  |  3 ++
>>  pc-bios/s390-ccw/start.S    | 62 +++++++++++++++++++++++++++----------
>>  3 files changed, 52 insertions(+), 17 deletions(-)
> 
> Patch looks basically fine to me, I just got some questions for my
> understanding below...
> 
>> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
>> index 5b8352d257..bb94ba7550 100644
>> --- a/pc-bios/s390-ccw/jump2ipl.c
>> +++ b/pc-bios/s390-ccw/jump2ipl.c
>> @@ -14,6 +14,7 @@
>>  #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
>>  #define RESET_PSW ((uint64_t)&jump_to_IPL_addr | RESET_PSW_MASK)
>>  
>> +extern uint64_t psw_save_io[], psw_save_ext[];
>>  static uint64_t *reset_psw = 0, save_psw, ipl_continue;
>>  
>>  void write_reset_psw(uint64_t psw)
>> @@ -59,6 +60,9 @@ void jump_to_IPL_code(uint64_t address)
>>      /* Ensure the guest output starts fresh */
>>      sclp_print("\n");
>>  
>> +    memcpy(&lowcore->io_new_psw, psw_save_io, 16);
>> +    memcpy(&lowcore->external_new_psw, psw_save_ext, 16);
>> +
>>      /*
>>       * HACK ALERT.
>>       * We use the load normal reset to keep r15 unchanged. jump_to_IPL_2
>> diff --git a/pc-bios/s390-ccw/netmain.c b/pc-bios/s390-ccw/netmain.c
>> index 056e93a818..74ef28fbc6 100644
>> --- a/pc-bios/s390-ccw/netmain.c
>> +++ b/pc-bios/s390-ccw/netmain.c
>> @@ -32,6 +32,7 @@
>>  #include <time.h>
>>  #include <pxelinux.h>
>>  
>> +#include "s390-arch.h"
>>  #include "s390-ccw.h"
>>  #include "cio.h"
>>  #include "virtio.h"
>> @@ -43,6 +44,8 @@
>>  extern char _start[];
>>  void write_iplb_location(void) {}
>>  
>> +LowCore *lowcore; /* Yes, this *is* a pointer to address 0 */
>> +
>>  #define KERNEL_ADDR             ((void *)0L)
>>  #define KERNEL_MAX_SIZE         ((long)_start)
>>  #define ARCH_COMMAND_LINE_SIZE  896              /* Taken from Linux kernel 
>> */
>> diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
>> index ce519300a1..939aac3a7c 100644
>> --- a/pc-bios/s390-ccw/start.S
>> +++ b/pc-bios/s390-ccw/start.S
>> @@ -34,7 +34,17 @@ remainder:
>>      larl    %r2,memsetxc
>>      ex      %r3,0(%r2)
>>  done:
>> -    j      main             /* And call C */
>> +        /* prepare i/o call handler */
>> +        larl  %r1, io_new_code
>> +        larl  %r2, io_new_psw
>> +        stg   %r1, 8(%r2)
>> +        mvc   0x1f0(16),0(%r2)
>> +        /* prepare external call handler */
>> +        larl  %r1, external_new_code
>> +        larl  %r2, external_new_psw
>> +        stg   %r1, 8(%r2)
> 
> Can't you specify the external_new_code and io_new_code in the
> external_new_psw / io_new_psw directly? Or is our relocation code not
> good enough for this?

Initially I had some problems with this. I just had another try and it
seems to work well, but as the testing infrastructure doesn't really
work, I can't vouch for that.

> 
>> +        mvc   0x1b0(16),0(%r2)
>> +        j      main         /* And call C */
>>  
>>  memsetxc:
>>      xc      0(1,%r1),0(%r1)
>> @@ -64,13 +74,16 @@ consume_sclp_int:
>>          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)
>> +        larl  %r1, external_new_psw
>> +        lghi  %r2, 0x1b0
>> +        /* Is the BIOS' external new PSW already set? */
>> +        clc   0(16, %r1), 0(%r2)
>> +        je    load_ewait
>> +        /* No, save old PSW and write BIOS PSW */
>> +        larl  %r3, psw_save_ext
>> +        mvc   0(16, %r3), 0x1b0
>> +        mvc   0x1b0(16),0(%r1)
>> +        j     load_ewait
>>  
>>  /*
>>   * void consume_io_int(void)
>> @@ -84,11 +97,20 @@ consume_io_int:
>>          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)
>> -        /* load enabled wait PSW */
>> +        larl  %r1, io_new_psw
>> +        lghi  %r2, 0x1f0
>> +        /* Is the BIOS' PSW already set? */
>> +        larl  %r3, load_ewait
>> +        clc   0(16, %r1), 0(%r2)
>> +        bcr   8, %r3
> 
> Why not a "je load_ewait" again, like in the consume_sclp_int handler?

Great question

> 
>> +        /* No, save old PSW and write BIOS PSW */
>> +        larl  %r3, psw_save_io
>> +        mvc   0(16, %r3), 0x1f0
>> +        mvc   0x1f0(16),0(%r1)
>> +        j     load_ewait
>> +
>> +load_ewait:
>> +        /* PSW is the correct one, time to load the enabled wait PSW */
>>          larl  %r1, enabled_wait_psw
>>          lpswe 0(%r1)
>>  
>> @@ -107,11 +129,17 @@ io_new_code:
>>          br    %r14
>>  
>>          .align  8
>> +        .globl psw_save_io
>> +        .globl psw_save_ext
>>  disabled_wait_psw:
>>          .quad   0x0002000180000000,0x0000000000000000
>>  enabled_wait_psw:
>>          .quad   0x0302000180000000,0x0000000000000000
>> -external_new_mask:
>> -        .quad   0x0000000180000000
>> -io_new_mask:
>> -        .quad   0x0000000180000000
>> +external_new_psw:
>> +        .quad   0x0000000180000000,0
>> +io_new_psw:
>> +        .quad   0x0000000180000000,0
>> +psw_save_io:
>> +        .quad   0,0
>> +psw_save_ext:
>> +        .quad   0,0
>>
> 
> In case you respin, could you maybe add some local #defines for 0x1f0
> and 0x1b0 ?

At the top of this file?

> 
>  Thomas
>

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