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Date:   Fri, 9 Sep 2022 14:08:04 +0800
From:   Chao Gao <chao.gao@intel.com>
To:     <isaku.yamahata@intel.com>
CC:     <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        Yuan Yao <yuan.yao@linux.intel.com>,
        <isaku.yamahata@gmail.com>, Kai Huang <kai.huang@intel.com>,
        Atish Patra <atishp@atishpatra.org>,
        Shaokun Zhang <zhangshaokun@hisilicon.com>,
        Qi Liu <liuqi115@huawei.com>,
        John Garry <john.garry@huawei.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        "Huang Ying" <ying.huang@intel.com>,
        Huacai Chen <chenhuacai@kernel.org>
Subject: Re: [PATCH v4 13/26] KVM: Add arch hook when VM is added/deleted
Message-ID: <YxrYRKeU/AfCVJFO@gao-cwp>
References: <cover.1662679124.git.isaku.yamahata@intel.com>
 <acc9a44a5626fa8d64690f3f6fcca6e85f6536cb.1662679124.git.isaku.yamahata@intel.com>
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On Thu, Sep 08, 2022 at 04:25:29PM -0700, isaku.yamahata@intel.com wrote:
>+__weak int kvm_arch_post_init_vm(struct kvm *kvm)

int __weak

>+{
>+	return 0;
>+}
>+
> /*
>  * Called after the VM is otherwise initialized, but just before adding it to
>  * the vm_list.
>  */
>-__weak int kvm_arch_post_init_vm(struct kvm *kvm)
>+__weak int kvm_arch_add_vm(struct kvm *kvm, int usage_count)
>+{
>+	return kvm_arch_post_init_vm(kvm);
>+}
>+
>+__weak int kvm_arch_del_vm(int usage_count)

ditto

>+static void kvm_del_vm(void)
>+{
>+	cpus_read_lock();
>+	mutex_lock(&kvm_lock);
>+	kvm_arch_del_vm(kvm_usage_count);
>+	mutex_unlock(&kvm_lock);
>+	cpus_read_unlock();

kvm_arch_del_vm() is an empty function now. I don't understand why
cpus_read_lock() is needed. Maybe add the lock when you fill up
kvm_arch_del_vm().