Re: [patch] kvm: make cr3 loading more robust

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Ingo Molnar wrote:
> another small detail is that currently KVM_SET_MEMORY_REGION appears to 
> be an add-only interface - it is not possible to 'unregister' RAM from a 
> VM.
>   

Well, the _interface_ supports removing, the implementation does not :)

Everything was written in mind to allow memory hotplug.

> That keeps things easy for now, but if it's ever implemented then the 
> current cr3 of all vcpus of the VM needs to be validated against the 
> reduced memory slot map. (besides migrating all existing mappings from 
> the removed memory slot to other memory slots and redirecting all 
> in-flight DMA transactions, etc., etc. Which all needs heavy guest-OS 
> awareness as well.)
>   

Actually I think it's quite easy:

- halt all vcpus
- wait for dma to complete
- mmu_free_roots()
- zap all page tables
- actually unplug memory
- mmu_alloc_roots()

The guest needs to cooperate, but it can do so using the native memory 
hotlpug mechanisms (whatever they are).  No guest modifications are needed.

-- 
error compiling committee.c: too many arguments to function


-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys - and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV