Re: [kvm-ppc-devel] RFC/patch portability: split kvm_vm_ioctl v2

Carsten Otte
2007-10-26T08:21:55Z

Avi Kivity wrote:
> Hollis Blanchard wrote:
>> On Fri, 2007-10-26 at 00:12 +0200, Izik Eidus wrote:
>>
>>> ok i was thinking,
>>> maybe we can rewrite the way kvm hold memory so more code would be shared,
>>> lets say we throw away all the slots and arch depended stuff, and we let kvm
>>> just hold the userspace allocated memory address,
>>>
>> With that approach, how would you create a sparse (guest physical)
>> memory map in userspace? I guess you would need to use repeated
>> mmap(MAP_FIXED), and that's starting to look very brittle.
>>
>>
>
> It can't work on i386 due to the limited host virtual address space.
That's why memory allocation/preparation needs to be arch dependent:
i386 needs a memory layout different from userspace page table due to
your argument, and s390 needs to use the userspace page table due to
hardware features we want to exploit.
As Xiantao pointed out, x86 and ia64 can share the same memory setup
code. But s390 and ppc don't. Therefore, I vote for putting it into
x86 for now, and come up with an approach to share between x86 and
ia64 later on.