Re: [RFC PATCH 0/3] generic hypercall support

Avi Kivity
2009-05-08T11:39:05Z

Marcelo Tosatti wrote:
>>> Also it would be interesting to see the MMIO comparison with EPT/NPT,
>>> it probably sucks much less than what you're seeing.
>>>
>>>
>> Why would NPT improve mmio? If anything, it would be worse, since the
>> processor has to do the nested walk.
>>
>
> I suppose the hardware is much more efficient than walk_addr? There's
> all this kmalloc, spinlock, etc overhead in the fault path.
>

mmio still has to do a walk_addr, even with npt. We don't take the mmu
lock during walk_addr.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.