Re: [PATCH v5 05/12] pc-bios: s390x: Remove unneeded dasd-ipl.c reset psw mask changes

[Thomas Huth]

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();
>   }