Re: [PATCH v3 07/15] KVM: MMU: introduce nulls desc

Marcelo Tosatti
2013-11-25T18:14:21Z

On Mon, Nov 25, 2013 at 02:29:03PM +0800, Xiao Guangrong wrote:
> >> Also, there is no guarantee of termination (as long as sptes are
> >> deleted with the correct timing). BTW, can't see any guarantee of
> >> termination for rculist nulls either (a writer can race with a lockless
> >> reader indefinately, restarting the lockless walk every time).
> >
> > Hmm, that can be avoided by checking dirty-bitmap before rewalk,
> > that means, if the dirty-bitmap has been set during lockless write-protection,
> > it�s unnecessary to write-protect its sptes. Your idea?
> This idea is based on the fact that the number of rmap is limited by
> RMAP_RECYCLE_THRESHOLD. So, in the case of adding new spte into rmap,
> we can break the rewalk at once, in the case of deleting, we can only
> rewalk RMAP_RECYCLE_THRESHOLD times.

Please explain in more detail.