Re: [Qemu-devel] QEMU savevm RAM page offsets

[Juerg Haefliger]

>>>> I didn't mean to imply that the savevm format is broken and needed
>>>> fixing. I was just wondering if the data is there and I simply hadn't
>>>> found it. Upgrading QEMU is not an option at the moment since these
>>>> are tightly controlled productions machines. Is it possible to loadvm
>>>> a savevm file from 1.0 with 1.6 to then use guest-memory-dump?
>>>
>>> Yes, it should, but one important thing since 1.0 has been the merger of
>>> qemu-kvm and QEMU.  What distribution are you using?  I know Fedora
>>> allows qemu-kvm-1.0 to QEMU-1.6 compatibility, but I don't know about
>>> others.
>>
>> Ubuntu 12.04
>>
>>
>>> Michael Tokarev is the maintainer of the Debian package, so he may be
>>> able to answer.
>>>
>>> Alternatively, you can modify your utility to simply add 512 MB to the
>>> addresses above 3.5 GB.
>>
>> Is it really as simple as that? Isn't the OS (particularly Windows)
>> possibly doing some crazy remapping that needs to be taken into
>> account? meminfo on a VM with 4GB running Windows 2008 shows the
>> following:
>>
>> C:\Users\Administrator\Desktop\MemInfo\amd64>MemInfo.exe -r
>> MemInfo v2.10 - Show PFN database information
>> Copyright (C) 2007-2009 Alex Ionescu
>> www.alex-ionescu.com
>>
>> Physical Memory Range: 0000000000001000 to 000000000009B000 (154 pages, 616 
>> KB)
>> Physical Memory Range: 0000000000100000 to 00000000DFFFD000 (917245
>> pages, 3668980 KB)
>> Physical Memory Range: 0000000100000000 to 0000000120000000 (131072
>> pages, 524288 KB)
>> MmHighestPhysicalPage: 1179648
>
> That should be fine, I think. The 384 KB hole between 640KB and 1MB is
> actually contiguously backed by RAMBlock, it is just not (necessarily)
> presented as conventional memory to the guest. You can treat the [0,
> 0x0e0000000) left-closed, right-open interval as contiguous.

Indeed simply adding a 512 MB hole between 3.5 GB and 4 GB did the
trick. Thanks a lot.


> Again, check out the diagram in 4/4 that I linked before. Compare it to
> pc_init1() in "hw/pc_piix.c", at tag "v1.0" in
> <git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git>. Look for the
> variable "below_4g_mem_size".

Nice diagram and very helpful.

Thanks
...Juerg


> Laszlo