Re: [Qemu-devel] [PATCH] spapr: make sure RMA is in first mode of first memory node

[Alexey Kardashevskiy]

On 11/04/2013 10:50 PM, Thomas Huth wrote:
> On Mon, 4 Nov 2013 12:28:12 +0100
> Alexander Graf <address@hidden> wrote:
> 
>>
>> On 04.11.2013, at 11:55, Benjamin Herrenschmidt <address@hidden> wrote:
>>
>>> On Mon, 2013-11-04 at 11:44 +0100, Alexander Graf wrote:
>>>> On 01.11.2013, at 11:21, Alexey Kardashevskiy <address@hidden> wrote:
>>>>
>>>>> SLOF gets really confused if RTAS/device-tree and everything else
>>>>> what SLOF can use is not in the very first block of the very first
>>>>> memory node.
>>>>>
>>>>> This makes sure that the RMA area is where SLOF expects it to be.
>>>>>
>>>>> Cc: Benjamin Herrenschmidt <address@hidden>
>>>>> Cc: Nikunj A Dadhania <address@hidden>
>>>>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>>>> ---
>>>>> hw/ppc/spapr.c | 8 +++++++-
>>>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>>>> index 09dc635..09a5d94 100644
>>>>> --- a/hw/ppc/spapr.c
>>>>> +++ b/hw/ppc/spapr.c
>>>>> @@ -1113,7 +1113,7 @@ static void ppc_spapr_init(QEMUMachineInitArgs 
>>>>> *args)
>>>>>    int i;
>>>>>    MemoryRegion *sysmem = get_system_memory();
>>>>>    MemoryRegion *ram = g_new(MemoryRegion, 1);
>>>>> -    hwaddr rma_alloc_size;
>>>>> +    hwaddr rma_alloc_size, node0_size;
>>>>>    uint32_t initrd_base = 0;
>>>>>    long kernel_size = 0, initrd_size = 0;
>>>>>    long load_limit, rtas_limit, fw_size;
>>>>> @@ -1154,6 +1154,12 @@ static void ppc_spapr_init(QEMUMachineInitArgs 
>>>>> *args)
>>>>>            spapr->rma_size = MIN(spapr->rma_size, 0x10000000);
>>>>>        }
>>>>>    }
>>>>> +    /*
>>>>> +     * SLOF gets confused if RMA resides not in the first block
>>>>> +     * of the first memory node so let's fix it.
>>>>> +     */
>>>>> +    node0_size = (nb_numa_nodes > 1) ? node_mem[0] : ram_size;
>>>>> +    spapr->rma_size = MIN(spapr->rma_size, node0_size);
>>>> So if I create a NUMA node of 4MB that will be my RMA? That sounds pretty 
>>>> broken, especially on 970.
>>>>
>>>> Why does SLOF have any issues with NUMA memory nodes? It can just ignore 
>>>> them, no?
>>>
>>> Because the only way SLOF knows about the RMA is by using the first
>>> "reg" entry of the first memory node and that's *all* SLOF knows about.
>>>
>>> If we start putting things like the DT, SLOF itself, etc... outside of
>>> that region, it will crash.
> 
> Ok, the question is whether this is a bug in SLOF and should be fixed
> there or whether the RMA should really be limited to the RAM of the
> first node only.


PAPR says in "Hypervisor Call Functions":

"Logical addresses start at zero. When control is initially passed to the
OS from the platform, the first region is the
single RMA. The first region has logical region identifier of zero. This
first region is specified by the first address -
length pair of the “reg” property of the /memory node of the OF device tree."


Question about english - is "the single RMA" equal to "the only RMA"?


> Looking at the function spapr_populate_memory(), it seems there is
> already similar code there, so I assume the RMA should really be
> limited to that size:
> 
>     /* memory node(s) */
>     node0_size = (nb_numa_nodes > 1) ? node_mem[0] : ram_size;
>     if (spapr->rma_size > node0_size) {
>         spapr->rma_size = node0_size;
>     }
> 
> Maybe this piece of code could just be done earlier instead, before
> setting up the fdt_addr and rtas_addr variables, instead of adding the
> similar piece of code of this patch?
> 
>>> So we "constrain" things to the rma that way.
>>>
>>> Creating 4M nodes makes no sense anyway
>>
>> So why don't we just use the "limit VRMA to 256MB" code always and error out 
>> of node0 is smaller? I don't think SLOF can run with less than 256MB anyway.
> 
> It's 128 MB nowadays ... there is even a define called MIN_RMA_SLOF for
> this in the code already.
> 
>  Thomas
> 


-- 
Alexey