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

[Thomas Huth <thuth@redhat.com>]

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.

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();
>  }