Re: [PATCH] pc-bios: s390x: Add a comment to the io and external new PSW setup

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 15.07.20 16:08, Janosch Frank wrote:
> Normally they don't need to be set up before waiting for an interrupt
> but are set up on boot. The BIOS however might overwrite the lowcore
> (and hence the PSWs) when loading a blob into memory and therefore
> needs to set up those PSWs more often.

Now when I read the new comment this actually inidicates a bug. 
When do we restore the original content? If the loaded program
does have interrupt handlers in the original image and relies on that
then we are broken, no?

> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  pc-bios/s390-ccw/start.S | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S
> index 01c4c21b26..b0fcb918cc 100644
> --- a/pc-bios/s390-ccw/start.S
> +++ b/pc-bios/s390-ccw/start.S
> @@ -64,7 +64,10 @@ consume_sclp_int:
>          stctg   %c0,%c0,0(%r15)
>          oi      6(%r15),0x2
>          lctlg   %c0,%c0,0(%r15)
> -        /* prepare external call handler */
> +        /*
> +         * Prepare external new PSW as it might have been overwritten
> +         * by a loaded blob
> +         */
>          larl %r1, external_new_code
>          stg %r1, 0x1b8
>          larl %r1, external_new_mask
> @@ -84,7 +87,10 @@ consume_io_int:
>          stctg %c6,%c6,0(%r15)
>          oi    4(%r15), 0xff
>          lctlg %c6,%c6,0(%r15)
> -        /* prepare i/o call handler */
> +        /*
> +         * Prepare i/o new PSW as it might have been overwritten
> +         * by a loaded blob
> +         */
>          larl  %r1, io_new_code
>          stg   %r1, 0x1f8
>          larl  %r1, io_new_mask
>