Re: [PATCH] KVM: x86/MMU: Zap non-leaf SPTEs when disabling dirty logging

[Paolo Bonzini]

On 5/26/22 16:30, Peter Xu wrote:
> On Thu, May 26, 2022 at 02:01:43PM +0200, Paolo Bonzini wrote:
> > On 5/26/22 01:09, Ben Gardon wrote:
> > > +		WARN_ON(max_mapping_level < iter.level);
> > > +
> > > +		/*
> > > +		 * If this page is already mapped at the highest
> > > +		 * viable level, there's nothing more to do.
> > > +		 */
> > > +		if (max_mapping_level == iter.level)
> > > +			continue;
> > > +
> > > +		/*
> > > +		 * The page can be remapped at a higher level, so step
> > > +		 * up to zap the parent SPTE.
> > > +		 */
> > > +		while (max_mapping_level > iter.level)
> > > +			tdp_iter_step_up(&iter);
> > > +
> > >    		/* Note, a successful atomic zap also does a remote TLB flush. */
> > > -		if (tdp_mmu_zap_spte_atomic(kvm, &iter))
> > > -			goto retry;
> > > +		tdp_mmu_zap_spte_atomic(kvm, &iter);
> > > +
> >
> > Can you make this a sparate function (for example
> > tdp_mmu_zap_collapsible_spte_atomic)?  Otherwise looks great!
>
> There could be a tiny downside of using a helper in that it'll hide the
> step-up of the iterator, which might not be as obvious as keeping it in the
> loop?

That's true, my reasoning is that zapping at a higher level can only be 
done by first moving the iterator up.  Maybe 
tdp_mmu_zap_at_level_atomic() is a better Though, I can very well apply 
this patch as is.

Paolo