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From: "Herongguang (Stephen)" <herongguang.he@huawei.com>
Message-ID: <58CFE56E.9090303@huawei.com>
Date: Mon, 20 Mar 2017 22:21:34 +0800
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Subject: [Qemu-devel] [BUG/RFC] INIT IPI lost when VM starts
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To: Paolo Bonzini <pbonzini@redhat.com>, rkrcmar@redhat.com, afaerber@suse.de, jan.kiszka@siemens.com, qemu-devel@nongnu.org, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, wangxinxin.wang@huawei.com, "weidong.huang@huawei.com >> Huangweidong (C)" <weidong.huang@huawei.com>

Hi,
We encountered a problem that when a domain starts, seabios failed to online a vCPU.

After investigation, we found that the reason is in kvm-kmod, KVM_APIC_INIT bit in
vcpu->arch.apic->pending_events was overwritten by qemu, and thus an INIT IPI sent
to AP was lost. Qemu does this since libvirtd sends a ‘query-cpus’ qmp command to qemu
on VM start.

In qemu, qmp_query_cpus-> cpu_synchronize_state-> kvm_cpu_synchronize_state->
do_kvm_cpu_synchronize_state, qemu gets registers/vcpu_events from kvm-kmod and
sets cpu->kvm_vcpu_dirty to true, and vcpu thread in qemu will call
kvm_arch_put_registers if cpu->kvm_vcpu_dirty is true, thus pending_events is
overwritten by qemu.

I think there is no need for qemu to set cpu->kvm_vcpu_dirty to true after ‘query-cpus’,
and  kvm-kmod should not clear KVM_APIC_INIT unconditionally. And I am not sure whether
it is OK for qemu to set cpu->kvm_vcpu_dirty in do_kvm_cpu_synchronize_state in each caller.

What’s your opinion?