Re: [PATCH v3 3/5] pc-bios: s390x: Use reset PSW if avaliable

[Thomas Huth]

On 31/08/2020 17.09, Janosch Frank wrote:
> If a blob provides a reset PSW then we should use it instead of
> branching to the PSW address and using our own mask.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  pc-bios/s390-ccw/bootmap.c  |  3 ++-
>  pc-bios/s390-ccw/jump2ipl.c | 22 +++++++++++++++++-----
>  pc-bios/s390-ccw/s390-ccw.h |  1 +
>  3 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
> index 8747c4ea26..5a03b1eb8b 100644
> --- a/pc-bios/s390-ccw/bootmap.c
> +++ b/pc-bios/s390-ccw/bootmap.c
> @@ -515,7 +515,8 @@ static void zipl_run(ScsiBlockPtr *pte)
>      IPL_assert(entry->component_type == ZIPL_COMP_ENTRY_EXEC, "No EXEC 
> entry");
>  
>      /* should not return */
> -    jump_to_IPL_code(entry->compdat.load_psw & PSW_MASK_SHORT_ADDR);
> +    write_reset_psw(entry->compdat.load_psw);
> +    jump_to_IPL_code(0);
>  }
>  
>  static void ipl_scsi(void)
> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
> index b6aad32def..5b8352d257 100644
> --- a/pc-bios/s390-ccw/jump2ipl.c
> +++ b/pc-bios/s390-ccw/jump2ipl.c
> @@ -12,15 +12,21 @@
>  
>  #define KERN_IMAGE_START 0x010000UL
>  #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
> +#define RESET_PSW ((uint64_t)&jump_to_IPL_addr | RESET_PSW_MASK)
>  
>  static uint64_t *reset_psw = 0, save_psw, ipl_continue;
>  
> +void write_reset_psw(uint64_t psw)
> +{
> +    *reset_psw = psw;
> +}
> +
>  static void jump_to_IPL_addr(void)
>  {
>      __attribute__((noreturn)) void (*ipl)(void) = (void *)ipl_continue;
>  
>      /* Restore reset PSW */
> -    *reset_psw = save_psw;
> +    write_reset_psw(save_psw);
>  
>      ipl();
>      /* should not return */
> @@ -43,9 +49,10 @@ void jump_to_IPL_code(uint64_t address)
>       * content of non-BIOS memory after we loaded the guest, so we
>       * save the original content and restore it in jump_to_IPL_2.
>       */
> -    save_psw = *reset_psw;
> -    *reset_psw = (uint64_t) &jump_to_IPL_addr;
> -    *reset_psw |= RESET_PSW_MASK;
> +    if (address) {
> +        save_psw = *reset_psw;
> +        write_reset_psw(RESET_PSW);
> +    }
>      ipl_continue = address;
>      debug_print_int("set IPL addr to", ipl_continue);

In case you respin this series, I think I'd move the "ipl_continue =
address" into the if-statement, too, and change the debug_print_int line
to use address instead of ipl_continue.

> @@ -77,7 +84,12 @@ void jump_to_low_kernel(void)
>  
>      /* Trying to get PSW at zero address */
>      if (*((uint64_t *)0) & RESET_PSW_MASK) {
> -        jump_to_IPL_code((*((uint64_t *)0)) & PSW_MASK_SHORT_ADDR);
> +        /*
> +         * Surely nobody will try running directly from lowcore, so
> +         * let's use 0 as an indication that we want to load the reset
> +         * psw at 0x0 and not jump to the entry.
> +         */
> +        jump_to_IPL_code(0);
>      }
>  
>      /* No other option left, so use the Linux kernel start address */
> diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
> index 36b884cced..7090720422 100644
> --- a/pc-bios/s390-ccw/s390-ccw.h
> +++ b/pc-bios/s390-ccw/s390-ccw.h
> @@ -78,6 +78,7 @@ int virtio_read(ulong sector, void *load_addr);
>  void zipl_load(void);
>  
>  /* jump2ipl.c */
> +void write_reset_psw(uint64_t psw);
>  void jump_to_IPL_code(uint64_t address);
>  void jump_to_low_kernel(void);

Looks sane to me:

Reviewed-by: Thomas Huth <thuth@redhat.com>