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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id u63sm5728603wmg.24.2021.03.31.14.36.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Mar 2021 14:36:36 -0700 (PDT) Subject: Re: [PATCH 16/18] KVM: Don't take mmu_lock for range invalidation unless necessary To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , James Morse , Julien Thierry , Suzuki K Poulose , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon References: <20210326021957.1424875-1-seanjc@google.com> <20210326021957.1424875-17-seanjc@google.com> <6e7dc7d0-f5dc-85d9-1c50-d23b761b5ff3@redhat.com> <56ea69fe-87b0-154b-e286-efce9233864e@redhat.com> <0e30625f-934d-9084-e293-cb3bcbc9e4b8@redhat.com> From: Paolo Bonzini Message-ID: <743a31e7-03ba-0c64-86ac-c5a0aac4121c@redhat.com> Date: Wed, 31 Mar 2021 23:36:34 +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: 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 23:22, Sean Christopherson wrote: > On a related topic, any preference on whether to have an explicit "must_lock" > flag (what I posted), or derive the logic based on other params? > > The helper I posted does: > > if (range->must_lock && > kvm_mmu_lock_and_check_handler(kvm, range, &locked)) > goto out_unlock; > > but it could be: > > if (!IS_KVM_NULL_FN(range->on_lock) && !range->may_block && > kvm_mmu_lock_and_check_handler(kvm, range, &locked)) > goto out_unlock; > > The generated code should be nearly identical on a modern compiler, so it's > purely a question of aesthetics. I slightly prefer the explicit "must_lock" to > avoid spreading out the logic too much, but it also feels a bit superfluous. I do as well, but I hope we don't need any lock after all as in the email I've just sent. Paolo