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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id ar1sm9969586ejc.30.2021.01.26.09.57.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Jan 2021 09:57:50 -0800 (PST) To: Vitaly Kuznetsov , Cun Li Cc: seanjc@google.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210111152435.50275-1-cun.jia.li@gmail.com> <87h7nn8ke8.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Subject: Re: [PATCH] KVM: update depracated jump label API Message-ID: <24e29c32-f6cb-cf7b-9376-1281b9545e69@redhat.com> Date: Tue, 26 Jan 2021 18:57:46 +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: <87h7nn8ke8.fsf@vitty.brq.redhat.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 11/01/21 18:15, Vitaly Kuznetsov wrote: > kvm_no_apic_vcpu is different, we actually need to increase it with > every vCPU which doesn't have LAPIC but maybe we can at least switch to > static_branch_inc()/static_branch_dec(). It is still weird we initialize > it to 'false' "kvm_no_apic_vcpu" is badly named. It reads as "true if no vCPU has APIC" but it means "true if some vCPU has no APIC". The latter is obviously false in the beginning, because there is no vCPUs at all. Perhaps a better name would be "kvm_has_noapic_vcpu" (for once, smashingwordstogether is more readable than the alternative). Paolo but it seems to be a documented behavior. From > include/linux/jump_label.h: > > "... Thus, static_branch_inc() can be thought of as a 'make more true' > and static_branch_dec() as a 'make more false'"