Re: [Qemu-devel] [PATCH] hw/arm/virt: Replace memory_region_init_ram with memory_region_allocate_system_memory

[Paolo Bonzini]

Il 14/10/2014 07:42, Peter Maydell ha scritto:
> On 14 October 2014 07:10, Paolo Bonzini <address@hidden> wrote:
>> Il 14/10/2014 06:54, Peter Maydell ha scritto:
>>> Why is this patch only changing this board? What's special
>>> about virt that means we don't want to also make this
>>> change for the other ARM boards? What about all the other
>>> boards for the other architectures?
>>
>> -mem-path is not too useful without KVM (TCG is too slow to
>> notice the difference.  PPC and S390 have already been fixed.
> 
> MIPS has KVM too now...

Yes.

>>> Incidentally I can't see anything that guards against
>>> calling memory_region_allocate_system_memory() twice,
>>> so I think you would end up with two blocks of RAM
>>> both backed by the same file then. Or have I misread
>>> the code?
>>
>> That would be a bug in the board, it is caught here:
>>
>>         if (memory_region_is_mapped(seg)) {
>>             char *path = 
>> object_get_canonical_path_component(OBJECT(backend));
>>             error_report("memory backend %s is used multiple times. Each "
>>                          "-numa option must use a different memdev value.",
>>                          path);
>>             exit(1);
>>         }
>>
>> The error message gives the common user error rather than
>> the less common developer error, but still you catch it.
> 
> That's only in the NUMA code path though, isn't it?
> I was looking at the non-numa codepath, which is what
> all the boards I care about are going to be taking :-)

The non-NUMA path will allocate memory from two separate files.
-mem-path takes a path, not a file.

> What's the right thing for a board where the system
> RAM isn't contiguous, by the way?

x86 allocates a big RAM region and uses aliases to split it into
non-contiguous areas.

Paolo