Re: [PATCH] do not free active mmu pages in free_mmu_pages()

Gleb Natapov
2009-03-16T21:23:58Z

On Mon, Mar 16, 2009 at 06:01:52PM -0300, Marcelo Tosatti wrote:
> On Mon, Mar 16, 2009 at 10:34:01PM +0200, Gleb Natapov wrote:
> > > Doesnt the vm shutdown path rely on the while loop you removed to free
> > > all shadow pages before freeing the mmu kmem caches, if mmu notifiers
> > > is disabled?
> > >
> > Shouldn't mmu_free_roots() on all vcpus clear all mmu pages?
>
> No. It only zaps the present root on every vcpu, but not
> the children.
>
> > > And how harmful is that loop? Zaps the entire cache on cpu hotunplug?
> > >
> > KVM doesn't support vcpu destruction, but destruction is called anyway
> > on various error conditions. The one that easy to trigger is to create
> > vcpu with the same id simultaneously from two threads. The result is
> > OOPs in random places.
>
> mmu_lock should be held there, and apparently it is not.
>
Yeah, my first solution was to add mmu_lock, but why function that gets
vcpu as an input should destroy data structure that is global for the VM.
There is kvm_mmu_zap_all() that does same thing (well almost) and also does
proper locking. Shouldn't it be called during VM destruction instead?

--
Gleb.