Re: [patch 3/4] KVM: MMU: reload request from GET_DIRTY_LOG path

[Gleb Natapov <gleb@kernel.org>]

On Wed, Oct 08, 2014 at 04:22:31PM -0300, Marcelo Tosatti wrote:
> > > 
> > > Argh, lets try again:
> > > 
> > > skip_pinned = true
> > > ------------------
> > > 
> > > mark page dirty, keep spte intact
> > > 
> > > called from get dirty log path.
> > > 
> > > skip_pinned = false
> > > -------------------
> > > reload remote mmu
> > > destroy pinned spte.
> > > 
> > > called from: dirty log enablement, rmap write protect (unused for pinned
> > > sptes)
> > > 
> > > 
> > > Note this behaviour is your suggestion:
> > 
> > Yes, I remember that and I thought we will not need this skip_pinned
> > at all.  For rmap write protect case there shouldn't be any pinned pages,
> > but why dirty log enablement sets skip_pinned to false? Why not mark
> > pinned pages as dirty just like you do in get dirty log path?
> 
> Because if its a large spte, it must be nuked (or marked read-only,
> which for pinned sptes, is not possible).
> 
If a large page has one small page pinned inside it its spte will
be marked as pinned, correct?  We did nuke large ptes here until very
recently: c126d94f2c90ed9d, but we cannot drop a pte here anyway without
kicking all vcpu from a guest mode, but do you need additional skip_pinned
parameter?  Why not check if spte is large instead?

So why not have per slot pinned page list (Xiao suggested the same) and do:

spte_write_protect() {
  if (is_pinned(spte) {
    if (large(spte))
       // cannot drop while vcpu are running
       mmu_reload_pinned_vcpus();
    else
       return false;
}
    

get_dirty_log() {
 for_each(pinned pages i)
    makr_dirty(i);
}

--
			Gleb.