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Date: Fri, 01 Feb 2008 17:13:37 +0200
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Subject: [Qemu-devel] Re: [PATCH 1/6] Use correct types to enable > 2G
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: kvm-devel@lists.sourceforge.net, Paul Brook <paul@codesourcery.com>, qemu-devel@nongnu.org

Anthony Liguori wrote:
> Fabrice Bellard wrote:
>> Anthony Liguori wrote:
>>> +    /* above 4giga memory allocation */
>>> +    if (above_4g_mem_size > 0) {
>>> +        ram_addr = qemu_ram_alloc(above_4g_mem_size);
>>> +        cpu_register_physical_memory(0x100000000, 
>>> above_4g_mem_size, ram_addr);
>>> +    }
>>> +
>>
>> Why do you need this ? All the RAM can be registered with a single 
>> call.  I fear you need to do that because of KVM RAM handling 
>> limitations.
>
> On the x86, there is a rather large hole at the top of memory.  
> Currently, we do separate allocations around this whole.    You can't 
> get away from doing multiple cpu_register_physical_memory calls here.  
> We've discussed just allocating a single chunk with qemu_ram_alloc 
> since so many places in QEMU assume that you can do phys_ram_base + PA.
>
> I think I'll change this too into a single qemu_ram_alloc.  That will 
> fix the bug with KVM when using -kernel and large memory anyway :-)

Won't that cause all of the memory in the hole to be wasted?

You could munmap() it, but it's hardly elegant.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.