Re: [PATCH RFC v2 3/4] pc-bios: s390x: Save io and external new PSWs before overwriting them

[Thomas Huth <thuth@redhat.com>]

On 27/08/2020 11.31, 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>
> ---
> 
> Maybe we should rather statically allocate a lowcore so we don't dirty
> 0x0 at all.
> 
> ---
>  pc-bios/s390-ccw/jump2ipl.c |  3 ++
>  pc-bios/s390-ccw/start.S    | 62 +++++++++++++++++++++++++++----------
>  2 files changed, 48 insertions(+), 17 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
> index 143d027bf7..a44f3ab5b3 100644
> --- a/pc-bios/s390-ccw/jump2ipl.c
> +++ b/pc-bios/s390-ccw/jump2ipl.c
> @@ -13,12 +13,15 @@
>  #define KERN_IMAGE_START 0x010000UL
>  #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
>  
> +extern uint64_t *psw_save_io, *psw_save_ext;

I think that should be

 extern uint64_t psw_save_io[], psw_save_ext[];

instead ... otherwise you'll end up with some funny bugs here, won't you?

>  uint64_t *reset_psw = 0, save_psw, ipl_continue;
>  
>  static void jump_to_IPL_2(void)
>  {
>      /* Restore reset PSW and io and external new PSWs */

Ok, now the comment makes sense :-)

>      *reset_psw = save_psw;
> +    memcpy((void *)0x1f0, psw_save_io, 16);
> +    memcpy((void *)0x1b0, psw_save_ext, 16);

Could you use &lowcore->external_new_psw and &lowcore->io_new_psw
instead of the magic numbers?

 Thomas