Re: [Qemu-devel] [qemu-s390x] [PATCH 1/1] s390x/sclp: fix maxram calculation

[Christian Borntraeger]

On 07/30/2018 04:34 PM, David Hildenbrand wrote:
> On 30.07.2018 16:09, Christian Borntraeger wrote:
>> We clamp down ram_size to match the sclp increment size. We do
>> not do the same for maxram_size, which means for large guests
>> with some sizes (e.g. -m 50000) maxram_size differs from ram_size.
>> This can break other code (e.g. CMMA migration) which uses maxram_size
>> to calculate the number of pages and then throws some errors.
> 
> So the only problem is that the buffer size between source and target
> differ?

The problem is that the target tries to access a non-existing buffer when 
committing all cmma value, so the kernel returns with EFAULT.
> 
>>
>> Fixes: 82fab5c5b90e468f3e9d54c ("s390x/sclp: remove memory hotplug support")
>> Signed-off-by: Christian Borntraeger <address@hidden>
>> CC: address@hidden
>> CC: David Hildenbrand <address@hidden>
>> ---
>>  hw/s390x/sclp.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index bd2a024..4510a80 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -320,6 +320,7 @@ static void sclp_memory_init(SCLPDevice *sclp)
>>      initial_mem = initial_mem >> increment_size << increment_size;
>>  
>>      machine->ram_size = initial_mem;
>> +    machine->maxram_size = initial_mem;
>>      /* let's propagate the changed ram size into the global variable. */
>>      ram_size = initial_mem;
>>  }
>>
> 
> I even have a private patch for that already :)