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.

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();
 }
-- 
2.25.1

On 24/06/2020 09.52, 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.

Hmm, the jump_to_IPL_code() also sets the 64-bit addressing bits ... but 
jump_to_low_kernel() has some logic that tests for the bits before that 
function is called:

     /* Trying to get PSW at zero address */
     if (*((uint64_t *)0) & RESET_PSW_MASK) {
         jump_to_IPL_code((*((uint64_t *)0)) & 0x7fffffff);
     }

Could it be that the code in dasd-ipl.c has been written with that 
if-statement in mind?

  Thomas


> 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();
>   }
> 

On 25/06/2020 12.57, Thomas Huth wrote:
> On 24/06/2020 09.52, 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.
> 
> Hmm, the jump_to_IPL_code() also sets the 64-bit addressing bits ... but 
> jump_to_low_kernel() has some logic that tests for the bits before that 
> function is called:
> 
>      /* Trying to get PSW at zero address */
>      if (*((uint64_t *)0) & RESET_PSW_MASK) {
>          jump_to_IPL_code((*((uint64_t *)0)) & 0x7fffffff);
>      }
> 
> Could it be that the code in dasd-ipl.c has been written with that 
> if-statement in mind?

... in that case, the code in dasd-ipl.c should maybe rather call 
jump_to_IPL_code((*((uint64_t *)0)) & 0x7fffffff) directly instead of 
going through jump_to_low_kernel(), I guess.

Jason, do you remember the intention here?

  Thomas