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[35.247.111.240]) by smtp.gmail.com with ESMTPSA id q11sm14597218pjq.6.2021.05.11.12.51.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 May 2021 12:51:30 -0700 (PDT) Date: Tue, 11 May 2021 19:51:26 +0000 From: Sean Christopherson To: Ben Gardon Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Peter Xu , Peter Shier , Yulei Zhang , Wanpeng Li , Xiao Guangrong , Kai Huang , Keqian Zhu , David Hildenbrand Subject: Re: [PATCH v4 6/7] KVM: x86/mmu: Skip rmap operations if rmaps not allocated Message-ID: References: <20210511171610.170160-1-bgardon@google.com> <20210511171610.170160-7-bgardon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210511171610.170160-7-bgardon@google.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, May 11, 2021, Ben Gardon wrote: > @@ -1260,9 +1268,12 @@ bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm, > int i; > bool write_protected = false; > > - for (i = PG_LEVEL_4K; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) { > - rmap_head = __gfn_to_rmap(gfn, i, slot); > - write_protected |= __rmap_write_protect(kvm, rmap_head, true); > + if (kvm->arch.memslots_have_rmaps) { > + for (i = PG_LEVEL_4K; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) { > + rmap_head = __gfn_to_rmap(gfn, i, slot); > + write_protected |= __rmap_write_protect(kvm, rmap_head, > + true); I vote to let "true" poke out. > + } > } > > if (is_tdp_mmu_enabled(kvm)) ... > @@ -5440,7 +5455,8 @@ static void kvm_mmu_zap_all_fast(struct kvm *kvm) > */ > kvm_reload_remote_mmus(kvm); > > - kvm_zap_obsolete_pages(kvm); > + if (kvm->arch.memslots_have_rmaps) > + kvm_zap_obsolete_pages(kvm); Hmm, for cases where we're iterating over the list of active_mmu_pages, I would prefer to either leave the code as-is or short-circuit the helpers with a more explicit: if (list_empty(&kvm->arch.active_mmu_pages)) return ...; I'd probably vote for leaving the code as it is; the loop iteration and list_empty check in kvm_mmu_commit_zap_page() add a single compare-and-jump in the worst case scenario. In other words, restrict use of memslots_have_rmaps to flows that directly walk the rmaps, as opposed to partially overloading memslots_have_rmaps to mean "is using legacy MMU". > write_unlock(&kvm->mmu_lock); > ... > @@ -5681,6 +5702,14 @@ void kvm_mmu_zap_all(struct kvm *kvm) > int ign; > > write_lock(&kvm->mmu_lock); > + if (is_tdp_mmu_enabled(kvm)) > + kvm_tdp_mmu_zap_all(kvm); > + > + if (!kvm->arch.memslots_have_rmaps) { > + write_unlock(&kvm->mmu_lock); > + return; Another case where falling through to walking active_mmu_pages is perfectly ok. > + } > + > restart: > list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) { > if (WARN_ON(sp->role.invalid)) > @@ -5693,9 +5722,6 @@ void kvm_mmu_zap_all(struct kvm *kvm) > > kvm_mmu_commit_zap_page(kvm, &invalid_list); > > - if (is_tdp_mmu_enabled(kvm)) > - kvm_tdp_mmu_zap_all(kvm); > - > write_unlock(&kvm->mmu_lock); > } > > -- > 2.31.1.607.g51e8a6a459-goog >