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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id y24sm3386648eds.23.2021.04.01.03.32.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Apr 2021 03:32:14 -0700 (PDT) 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> <20210202185734.1680553-21-bgardon@google.com> From: Paolo Bonzini Subject: Re: [PATCH v2 20/28] KVM: x86/mmu: Use atomic ops to set SPTEs in TDP MMU map Message-ID: Date: Thu, 1 Apr 2021 12:32:13 +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: <20210202185734.1680553-21-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: > @@ -720,7 +790,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code, > */ > if (is_shadow_present_pte(iter.old_spte) && > is_large_pte(iter.old_spte)) { > - tdp_mmu_set_spte(vcpu->kvm, &iter, 0); > + if (!tdp_mmu_set_spte_atomic(vcpu->kvm, &iter, 0)) > + break; > > kvm_flush_remote_tlbs_with_address(vcpu->kvm, iter.gfn, > KVM_PAGES_PER_HPAGE(iter.level)); > > /* > * The iter must explicitly re-read the spte here > * because the new value informs the !present > * path below. > */ > iter.old_spte = READ_ONCE(*rcu_dereference(iter.sptep)); > } > > if (!is_shadow_present_pte(iter.old_spte)) { Would it be easier to reason about this code by making it retry, like: retry: if (is_shadow_present_pte(iter.old_spte)) { if (is_large_pte(iter.old_spte)) { if (!tdp_mmu_zap_spte_atomic(vcpu->kvm, &iter)) break; /* * The iter must explicitly re-read the SPTE because * the atomic cmpxchg failed. */ iter.old_spte = READ_ONCE(*rcu_dereference(iter.sptep)); goto retry; } } else { ... } ? Paolo