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

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Message-ID: <Yo+O6AqNNBTg7BMY@xz-m1.local>
Date:   Thu, 26 May 2022 10:30:00 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Ben Gardon <bgardon@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH] KVM: x86/MMU: Zap non-leaf SPTEs when disabling dirty
 logging

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?

Thanks,

-- 
Peter Xu