Re: [kvm-devel] [RFC] [VTD][patch 1/3] vt-d support for pci passthrough: kvm-vtd--kernel.patch

[Avi K. <av...@qu...>]

Anthony Liguori wrote:
>> I don't think we can do page migration with VT-d.  You need to be able 
>> to detect whether the page has been changed by dma after you've copied 
>> it but before you changed the pte, but VT-d doesn't allow that AFAICT.
>>     
>
> Hrm, I would have to look at the VT-d but I suspect you're right.  
> That's unfortunate.
>
> That means mlock() isn't sufficient.  It also means that the VMAs can't 
> be updated while the guest is running.  Is there any way to lock a vma 
> region such that things like madvise/mmap(MAP_FIXED) will always fail?
>   

Userspace can simply not issue them.  Page migration is also controlled 
by userspace.

Once active memory defragmentation goes in, we need a way to tell the 
kernel that the allocation is unreclaimable, perhaps with a new mmap flag.

-- 
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