Messages in this thread | | | Subject | Re: [PATCH 2/2] KVM: x86/mmu: Don't step down in the TDP iterator when zapping all SPTEs | From | Paolo Bonzini <> | Date | Thu, 12 Aug 2021 19:38:43 +0200 |
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On 12/08/21 19:33, Sean Christopherson wrote: > On Thu, Aug 12, 2021, Paolo Bonzini wrote: >> On 12/08/21 19:07, Sean Christopherson wrote: >>> Yeah, I was/am on the fence too, I almost included a blurb in the cover letter >>> saying as much. I'll do that for v2 and let Paolo decide. >> >> I think it makes sense to have it. You can even use the ternary operator > > Hah, yeah, I almost used a ternary op. Honestly don't know why I didn't, guess > my brain flipped a coin. > >> >> /* >> * When zapping everything, all entries at the top level >> * ultimately go away, and the levels below go down with them. >> * So do not bother iterating all the way down to the leaves. > > The subtle part is that try_step_down() won't actually iterate down because it > explicitly rereads and rechecks the SPTE. > > if (iter->level == iter->min_level) > return false; > > /* > * Reread the SPTE before stepping down to avoid traversing into page > * tables that are no longer linked from this entry. > */ > iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); \ > ---> this is the code that is avoided > child_pt = spte_to_child_pt(iter->old_spte, iter->level); / > if (!child_pt) > return false;
Ah, right - so I agree with Ben that it's not too important.
Paolo
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