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Re: [PATCH v2 2/4] pc-bios: s390x: Use reset PSW if avaliable
From: |
Thomas Huth |
Subject: |
Re: [PATCH v2 2/4] pc-bios: s390x: Use reset PSW if avaliable |
Date: |
Thu, 27 Aug 2020 14:43:20 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 |
On 27/08/2020 11.31, 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 | 1 +
> pc-bios/s390-ccw/jump2ipl.c | 48 ++++++++++++++++++++++---------------
> pc-bios/s390-ccw/s390-ccw.h | 1 +
> 3 files changed, 31 insertions(+), 19 deletions(-)
>
> diff --git a/pc-bios/s390-ccw/bootmap.c b/pc-bios/s390-ccw/bootmap.c
> index 8747c4ea26..0df9b3781d 100644
> --- a/pc-bios/s390-ccw/bootmap.c
> +++ b/pc-bios/s390-ccw/bootmap.c
> @@ -515,6 +515,7 @@ static void zipl_run(ScsiBlockPtr *pte)
> IPL_assert(entry->component_type == ZIPL_COMP_ENTRY_EXEC, "No EXEC
> entry");
>
> /* should not return */
> + write_reset_psw(entry->compdat.load_psw);
> jump_to_IPL_code(entry->compdat.load_psw & PSW_MASK_SHORT_ADDR);
Shouldn't that be jump_to_IPL_code(0) now? Wouldn't it be cleaner to
have a jump_to_IPL_PSW() function instead?
> }
>
> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
> index 767012bf0c..143d027bf7 100644
> --- a/pc-bios/s390-ccw/jump2ipl.c
> +++ b/pc-bios/s390-ccw/jump2ipl.c
> @@ -13,20 +13,28 @@
> #define KERN_IMAGE_START 0x010000UL
> #define RESET_PSW_MASK (PSW_MASK_SHORTPSW | PSW_MASK_64)
>
> -typedef struct ResetInfo {
> - uint64_t ipl_psw;
> - uint32_t ipl_continue;
> -} ResetInfo;
> -
> -static ResetInfo save;
> +uint64_t *reset_psw = 0, save_psw, ipl_continue;
I think the patch would be better readable if you'd split it in two -
first the ResetInfo rework, then the use-reset-PSW-if-available stuff ?
> static void jump_to_IPL_2(void)
> {
> - ResetInfo *current = 0;
> + /* Restore reset PSW and io and external new PSWs */
> + *reset_psw = save_psw;
The comment talks about io and external new PSWs ... but where is it in
the code?
> - void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue;
> - *current = save;
> - ipl(); /* should not return */
> + /* No reset PSW, let's jump instead. */
> + if (ipl_continue) {
> + void (*ipl)(void) = (void *) (uint64_t) ipl_continue;
Is it possible to mark a function pointer with __attribute__((noreturn)) ?
> + ipl();
> + }
> +
> + /* Reset PSW available, let's load it */
> + asm volatile ("lpsw 0(%0)\n"
> + : : "a" (0):);
I've never tried. but maybe you could add __attribute__((noreturn)) to
an inline asm statement, too?
> + /* should not return */
> +}
> +
> +void write_reset_psw(uint64_t psw)
> +{
> + *reset_psw = psw;
> }
>
> void jump_to_IPL_code(uint64_t address)
> @@ -46,15 +54,12 @@ 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.
> */
> - ResetInfo *current = 0;
> + save_psw = *reset_psw;
> + *reset_psw = (uint64_t) &jump_to_IPL_2;
> + *reset_psw |= RESET_PSW_MASK;
> + ipl_continue = address;
>
> - save = *current;
> -
> - current->ipl_psw = (uint64_t) &jump_to_IPL_2;
> - current->ipl_psw |= RESET_PSW_MASK;
> - current->ipl_continue = address & PSW_MASK_SHORT_ADDR;
> -
> - debug_print_int("set IPL addr to", current->ipl_continue);
> + debug_print_int("set IPL addr to", ipl_continue);
>
> /* Ensure the guest output starts fresh */
> sclp_print("\n");
> @@ -84,7 +89,12 @@ 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);
>
>
Thomas