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From: Wanpeng Li <kernellwp@gmail.com>
Date: Thu, 7 Jul 2016 16:31:31 +0800
Message-ID: <CANRm+CySe7gcSgoyX2ZRijfUNNtQuT+WW1K5baDHSP8acyYMsw@mail.gmail.com>
Subject: Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02
 even if L1 doesn't enable it
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        kvm <kvm@vger.kernel.org>, Wanpeng Li <wanpeng.li@hotmail.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Yunhong Jiang <yunhong.jiang@intel.com>,
        Jan Kiszka <jan.kiszka@siemens.com>,
        Haozhong Zhang <haozhong.zhang@intel.com>
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2016-07-07 16:10 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 07/07/2016 05:46, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>
>> We will go to vcpu_run() loop after L0 emulates VMRESUME which incurs
>> kvm_sched_out and kvm_sched_in operations since cond_resched() will be
>> called once need resched. Preemption timer will be reprogrammed if vCPU
>> is scheduled to a different pCPU. Then the preemption timer bit of vmcs02
>> will be set if L0 enable preemption timer to run L1 even if L1 doesn't
>> enable preemption timer to run L2.
>>
>> This patch fix it by don't reprogram preemption timer of vmcs02 if L1's
>> vCPU is scheduled on diffent pCPU when we are in the way to vmresume
>> nested guest.
>
> Again, this is wrong.  There is no reason why L1's APIC timer cannot be
> emulated through the vmcs12's preemption timer setting.  The only issue
> is getting the pin-based execution controls right.

This patch doesn't intend to implement "L1 TSC deadline timer to
trigger while L2 is running", it just solves why vmcs02 is set even if

exec_control = vmcs12->pin_based_vm_exec_control;
exec_control |= vmcs_config.pin_based_exec_ctrl;
exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;

We should set pin-based execution controls right to implement "L1 TSC
deadline timer to trigger while L2 is running".

Regards,
Wanpeng Li