[SLOF] [PATCH slof] rtas: Reserve space for FWNMI log

[Alexey Kardashevskiy]

On 26/08/2019 22:29, Thomas Huth wrote:
> On 26/08/2019 05.44, Alexey Kardashevskiy wrote:
>> The Firmware Assisted Non-Maskable Interrupts Option (FWNMI) feature
>> requires some space for RTAS log which is in the RTAS blob area.
>>
>> This expands the RTAS blob size to 2k.
>>
>> More details here: https://patchwork.ozlabs.org/patch/1146765/
> 
> Ouch, that sounds like an very fragile interface. Is this mandated by
> sPAPR that we have to put the log into the RTAS region?


This is my understanding, yes. Aravinda can correct me if I am wrong. 
QEMU uses a fixed offset of 0x30 into this area to decide where the log 
starts. Not perfect but the frequency of RTAS changes (which a naught) 
assumes we are quite safe here.

> 
>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>> ---
>>   lib/libhvcall/hvcall.S | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/lib/libhvcall/hvcall.S b/lib/libhvcall/hvcall.S
>> index b19f6dbeff2c..adcda0dd905d 100644
>> --- a/lib/libhvcall/hvcall.S
>> +++ b/lib/libhvcall/hvcall.S
>> @@ -134,6 +134,7 @@ ENTRY(hv_rtas)
>>   	ori	r3,r3,KVMPPC_H_RTAS at l
>>   	HVCALL
>>   	blr
>> +	.space 2048 - (. - hv_rtas)
>>   	.globl hv_rtas_size
>>   hv_rtas_size:
>>   	.long . - hv_rtas;
>> @@ -144,6 +145,7 @@ ENTRY(hv_rtas_broken_sc1)
>>   	ori	r3,r3,KVMPPC_H_RTAS at l
>>   	.long	0x7c000268
>>   	blr
>> +	.space 2048 - (. - hv_rtas_broken_sc1)
>>   	.globl hv_rtas_broken_sc1_size
>>   hv_rtas_broken_sc1_size:
>>   	.long . - hv_rtas_broken_sc1;
>>
> 
> Can you please at least add some comments to the code which explain the
> padding - otherwise it's pretty impossible to understand when you look
> at the code later.

Sure can do that, how about:

/*
  * A space reserved for a RTAS log from Firmware Assisted
  * Non-Maskable Interrupts Option (FWNMI) feature.
  *
  * The QEMU implementation uses 0x30..0x800 for the log.
  */

?


-- 
Alexey