Re: [Qemu-devel] [Qemu-ppc] [PATCH v3 1/4] target-ppc: Extend rtas-blob

[Aravinda Prasad]

On Wednesday 05 November 2014 02:37 PM, Alexander Graf wrote:
> 
> 
> On 05.11.14 10:00, Alexander Graf wrote:
>>
>>
>> On 05.11.14 09:46, Aravinda Prasad wrote:
>>>
>>>
>>> On Wednesday 05 November 2014 01:41 PM, Alexander Graf wrote:
>>>>
>>>>
>>>> On 05.11.14 08:12, Aravinda Prasad wrote:
>>>>> Extend rtas-blob to accommodate error log. Error log
>>>>> structure is saved in rtas space upon a machine check
>>>>> exception.
>>>>>
>>>>> Signed-off-by: Aravinda Prasad <address@hidden>
>>>>> ---
>>>>>  hw/ppc/spapr.c         |    7 +++++++
>>>>>  include/hw/ppc/spapr.h |    5 +++++
>>>>>  2 files changed, 12 insertions(+)
>>>>>
>>>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>>>> index 30de25d..38e26af 100644
>>>>> --- a/hw/ppc/spapr.c
>>>>> +++ b/hw/ppc/spapr.c
>>>>> @@ -1431,6 +1431,13 @@ static void ppc_spapr_init(MachineState *machine)
>>>>>  
>>>>>      filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, "spapr-rtas.bin");
>>>>>      spapr->rtas_size = get_image_size(filename);
>>>>> +
>>>>> +    /*
>>>>> +     * Resize blob to accommodate error log. The layout of the rtas
>>>>> +     * blob is defined in include/hw/ppc/spapr.h
>>>>> +     */
>>>>> +    spapr->rtas_size = TARGET_PAGE_ALIGN(spapr->rtas_size);
>>>>
>>>> How big is the error log? You could just extend the RTAS blob to include
>>>> space for it if it's not too big.
>>>
>>> Error log is around 10 bytes and requires additional 24 bytes to store
>>> saved sro/srr1.
>>>
>>> Hmm.. yes it can be included in RTAS blob itself.
>>>
>>>
>>>>
>>>>> +
>>>>>      spapr->rtas_blob = g_malloc(spapr->rtas_size);
>>>>>      if (load_image_size(filename, spapr->rtas_blob, spapr->rtas_size) < 
>>>>> 0) {
>>>>>          hw_error("qemu: could not load LPAR rtas '%s'\n", filename);
>>>>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>>>>> index 749daf4..d08fcc2 100644
>>>>> --- a/include/hw/ppc/spapr.h
>>>>> +++ b/include/hw/ppc/spapr.h
>>>>> @@ -480,4 +480,9 @@ int spapr_dma_dt(void *fdt, int node_off, const char 
>>>>> *propname,
>>>>>  int spapr_tcet_dma_dt(void *fdt, int node_off, const char *propname,
>>>>>                        sPAPRTCETable *tcet);
>>>>>  
>>>>> +/* RTAS Blob layout in memory */
>>>>> +#define RTAS_ENTRY_OFFSET        0
>>>>> +#define RTAS_TRAMPOLINE_OFFSET   0x200
>>>>> +#define RTAS_ERRLOG_OFFSET       0x800
>>>>
>>>> I thought we agreed that these offsets should've been defined by the
>>>> blob itself?
>>>>
>>>
>>> I think I got it wrong.
>>>
>>> I will include these indexes at the entry of RTAS blob. With that we
>>> will have something like this:
>>>
>>> RTAS_ENTRY_OFFSET  =      *(spapr->rtas_addr)
>>> RTAS_TRAMPOLINE_OFFSET =  *(spapr->rtas_addr+8)
>>> RTAS_ERRLOG_OFFSET =      *(spapr->rtas_addr+16)
>>>
>>> I will fix this.
>>
>> Cool :). Just store the offsets inside of a helper struct that you for
>> example store in the spapr struct, then we don't need to read volatile
>> guest memory for the offsets.
> 
> I just reread what I wrote and figured it's not exactly verbose. What I
> meant was that you read them on load into a struct. Then when working
> with the offsets, you only use the cached ones from the struct.
> 
> That way when the guest for whatever reason modifies the RTAS blob in
> memory, we would still use the old offsets and ensure that we don't end
> up overwriting memory that we never intended to overwrite ;).

sure

> 
> 
> Alex
> 

-- 
Regards,
Aravinda