Re: [PATCH v2 14/27] KVM: x86: Reject memslot MOVE operations if KVMGT is attached

[Yan Zhao]

On Wed, Mar 15, 2023 at 08:43:54AM -0700, Sean Christopherson wrote:
> > So, in theory, the new GFNs are not write tracked though the old ones are.
> > 
> > Is that acceptable for the internal page-track user?
> 
> It works because KVM zaps all SPTEs when a memslot is moved, i.e. the fact that
Oh, yes!
And KVM will not shadow SPTEs for a invalid memslot, so there's no
problem.
Thanks~

> KVM loses the write-tracking counts is benign.  I suspect no VMM actually does
> does KVM_MR_MOVE in conjunction with shadow paging, but the ongoing maintenance
> cost of supporting KVM_MR_MOVE is quite low at this point, so trying to rip it
> out isn't worth the pain of having to deal with potential ABI breakage.
> 
> Though in hindsight I wish I had tried disallowed moving memslots instead of
> fixing the various bugs a few years back. :-(