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

Avi Kivity
2007-10-26T09:08:30Z

Carsten Otte wrote:
> 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.
>

But can't s390 and ppc use a subset? If you limit the number of memory
slots to one, it's equivalent to base + limit.

No?

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