Re: [RFC v5 12/12] pc-bios: s390x: Cleanup jump to ipl code

[Janosch Frank]

On 6/25/20 2:58 PM, Thomas Huth wrote:
> On 24/06/2020 09.52, Janosch Frank wrote:
>> jump_to_IPL_code takes a 64 bit address, masks it with the short psw
>> address mask and later branches to it using a full 64 bit register.
>>
>> * As the masking is not necessary, let's remove it
>> * Without the mask we can save the ipl address to a static 64 bit
>>    function ptr as we later branch to it
>> * Let's also clean up the variable names and remove the now unneeded
>>    ResetInfo
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>   pc-bios/s390-ccw/jump2ipl.c | 27 +++++++++++----------------
>>   1 file changed, 11 insertions(+), 16 deletions(-)
>>
>> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c
>> index 767012bf0c..aef37cea76 100644
>> --- a/pc-bios/s390-ccw/jump2ipl.c
>> +++ b/pc-bios/s390-ccw/jump2ipl.c
>> @@ -13,20 +13,15 @@
>>   #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;
>> +static void (*ipl_continue)(void);
>> +static uint64_t psw_save;
> 
> I wonder whether there was a reason for having ipl_continue in the 
> lowcore instead of using a simple static function pointer... Christian, 
> do you remember?
> 
>>   static void jump_to_IPL_2(void)
>>   {
>> -    ResetInfo *current = 0;
>> +    uint64_t *psw_current = 0;
> 
> Mhh, what about using uint64_t *psw_current = (uint64_t *)lowcore 
> instead, to make it more more explicit?

Sure, that would make it way better to read.

> 
>> -    void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue;
>> -    *current = save;
>> -    ipl(); /* should not return */
>> +    *psw_current = psw_save;
>> +    ipl_continue(); /* should not return */
>>   }
>>   
>>   void jump_to_IPL_code(uint64_t address)
>> @@ -46,15 +41,15 @@ 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;
>> +    uint64_t *psw_current = 0;
> 
> dito.
> 
>> -    save = *current;
>> +    psw_save = *psw_current;
>>   
>> -    current->ipl_psw = (uint64_t) &jump_to_IPL_2;
>> -    current->ipl_psw |= RESET_PSW_MASK;
>> -    current->ipl_continue = address & PSW_MASK_SHORT_ADDR;
>> +    *psw_current = (uint64_t) &jump_to_IPL_2;
>> +    *psw_current |= RESET_PSW_MASK;
>> +    ipl_continue = (void *)address;
>>   
>> -    debug_print_int("set IPL addr to", current->ipl_continue);
>> +    debug_print_int("set IPL addr to", (uint64_t)ipl_continue);
>>   
>>       /* Ensure the guest output starts fresh */
>>       sclp_print("\n");
>>
> 
> The patch sounds like a good idea to me ... but since this code proofed 
> to be very fragile in the past, let's wait for Christian to say whether 
> there was a good reason for ipl_continue in the lowcore or not.

This is a RFC and will need a lot of testing.
I guess I'll move patch 11 and 12 of this series into a new one and also
fix some more boot related stuff so this becomes less maze like.

> 
>   Thomas
> 
>

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