Re: [PATCH] QEMU support for virtio balloon driver

[Marcelo Tosatti <marcelo@kvack.org>]

On Sat, Mar 08, 2008 at 04:27:13PM -0300, Marcelo Tosatti wrote:
> On Sat, Jan 26, 2008 at 08:47:28PM +0200, Avi Kivity wrote:
> > Anthony Liguori wrote:
> > >Do others expect KVM to just cope with the virtual mapping being changed 
> > >out from underneath of it?
> > >  
> > 
> > kvm should cope with both malicious guests and malicious (or buggy) host 
> > userspace.  It's difficuly to analyze, but mmu notifiers might be 
> > necessary for the latter.
> 
> The reason for the host crash with madvise is that the rmap code relies
> on the guest process virtual mappings from not disappearing while there
> are active shadow mappings.
> 
> How to proceed now? Do we want to efficiently support ballooning without
> mmu notifiers? If so, an ioctl to zap the mmu is necessary as discussed
> before.

Err, actually zapping the mmu is necessary to guarantee guest will not
use stale shadow entries vs entries pointing to old unreacheable pages.

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