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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id p9sm3187071eds.66.2021.04.01.02.37.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Apr 2021 02:37:13 -0700 (PDT) Subject: Re: [PATCH 08/13] KVM: x86/mmu: Protect the tdp_mmu_roots list with RCU 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: <20210331210841.3996155-1-bgardon@google.com> <20210331210841.3996155-9-bgardon@google.com> From: Paolo Bonzini Message-ID: Date: Thu, 1 Apr 2021 11:37:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210331210841.3996155-9-bgardon@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/03/21 23:08, Ben Gardon wrote: > Protect the contents of the TDP MMU roots list with RCU in preparation > for a future patch which will allow the iterator macro to be used under > the MMU lock in read mode. > > Signed-off-by: Ben Gardon > --- > arch/x86/kvm/mmu/tdp_mmu.c | 64 +++++++++++++++++++++----------------- > 1 file changed, 36 insertions(+), 28 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > + spin_lock(&kvm->arch.tdp_mmu_pages_lock); > + list_del_rcu(&root->link); > + spin_unlock(&kvm->arch.tdp_mmu_pages_lock); Please update the comment above tdp_mmu_pages_lock in arch/x86/include/asm/kvm_host.h as well. > /* Only safe under the MMU lock in write mode, without yielding. */ > #define for_each_tdp_mmu_root(_kvm, _root) \ > - list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link) > + list_for_each_entry_rcu(_root, &_kvm->arch.tdp_mmu_roots, link, \ > + lockdep_is_held_write(&kvm->mmu_lock)) This should also add "... || lockdep_is_help(&kvm->arch.tdp_mmu_pages_lock)", if only for documentation purposes. Paolo