Re: KVM nonblocking MMU notifier with KVM_GUEST_USES_PFN looks racy [but is currently unused]

[Sean Christopherson]

On Mon, Sep 18, 2023, Jann Horn wrote:
> Hi!
> 
> I haven't tested this and might be missing something, but I think that
> the MMU notifier for KVM_GUEST_USES_PFN pfncache is currently a bit
> broken. Except that nothing seems to actually use KVM_GUEST_USES_PFN,
> so currently it's not actually a problem?

Yeah, the implementation is busted, and IMO the entire concept is a dead-end[1].
David Steven's series[2] doesn't actually rip out KVM_GUEST_USES_PFN, I'll add
that to the todo list.  There are no users, and I don't expect any to come along,
precisely because it's busted :-)

[1] https://lore.kernel.org/all/ZBEEQtmtNPaEqU1i@xxxxxxxxxx
[2] https://lkml.kernel.org/r/20230911021637.1941096-1-stevensd%40google.com