Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spteand mmu notifier to help KSM dirty bit tracking

[Avi Kivity]

On 06/22/2011 02:05 PM, Izik Eidus wrote:
> > > +    spte = rmap_next(kvm, rmapp, NULL);
> > > +    while (spte) {
> > > +        int _dirty;
> > > +        u64 _spte = *spte;
> > > +        BUG_ON(!(_spte&  PT_PRESENT_MASK));
> > > +        _dirty = _spte&  PT_DIRTY_MASK;
> > > +        if (_dirty) {
> > > +            dirty = 1;
> > > +            clear_bit(PT_DIRTY_SHIFT, (unsigned long *)spte);
> > > +        }
> >
> > Racy.  Also, needs a tlb flush eventually.
> +
>
> Hi, one of the issues is that the whole point of this patch is not do 
> tlb flush eventually,
> But I see your point, because other users will not expect such 
> behavior, so maybe there is need into a parameter
> flush_tlb=?, or add another mmu notifier call?

If you don't flush the tlb, a subsequent write will not see that spte.d 
is clear and the write will happen.  So you'll see the page as clean 
even though it's dirty.  That's not acceptable.

--
error compiling committee.c: too many arguments to function

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