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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id f6sm741435edk.13.2021.02.03.03.34.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Feb 2021 03:34:26 -0800 (PST) To: Ben Gardon , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Peter Xu , Sean Christopherson , Peter Shier , Peter Feiner , Junaid Shahid , Jim Mattson , Yulei Zhang , Wanpeng Li , Vitaly Kuznetsov , Xiao Guangrong References: <20210202185734.1680553-1-bgardon@google.com> <20210202185734.1680553-26-bgardon@google.com> From: Paolo Bonzini Subject: Re: [PATCH v2 25/28] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU read lock Message-ID: Date: Wed, 3 Feb 2021 12:34:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210202185734.1680553-26-bgardon@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/02/21 19:57, Ben Gardon wrote: > @@ -1485,7 +1489,9 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm, > struct kvm_mmu_page *root; > int root_as_id; > > - for_each_tdp_mmu_root_yield_safe(kvm, root, false) { > + read_lock(&kvm->mmu_lock); > + > + for_each_tdp_mmu_root_yield_safe(kvm, root, true) { > root_as_id = kvm_mmu_page_as_id(root); > if (root_as_id != slot->as_id) > continue; > @@ -1493,6 +1499,8 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm, > zap_collapsible_spte_range(kvm, root, slot->base_gfn, > slot->base_gfn + slot->npages); > } > + > + read_unlock(&kvm->mmu_lock); > } I'd prefer the functions to be consistent about who takes the lock, either mmu.c or tdp_mmu.c. Since everywhere else you're doing it in mmu.c, that would be: diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 0554d9c5c5d4..386ee4b703d9 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5567,10 +5567,13 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm, write_lock(&kvm->mmu_lock); slot_handle_leaf(kvm, (struct kvm_memory_slot *)memslot, kvm_mmu_zap_collapsible_spte, true); + write_unlock(&kvm->mmu_lock); - if (kvm->arch.tdp_mmu_enabled) + if (kvm->arch.tdp_mmu_enabled) { + read_lock(&kvm->mmu_lock); kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot); - write_unlock(&kvm->mmu_lock); + read_unlock(&kvm->mmu_lock); + } } void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm, and just lockdep_assert_held_read here. > - tdp_mmu_set_spte(kvm, &iter, 0); > - > - spte_set = true; Is it correct to remove this assignment? Paolo