linux-kernel - Re: [PATCH] KVM: VMX: Check if bus lock vmexit was preempted

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Message-ID: <84cd2713-3cc4-3120-946e-0cf8b8a8187d@linux.alibaba.com>
Date:   Thu, 23 Sep 2021 08:59:11 +0800
From:   Hao Xiang <hao.xiang@...ux.alibaba.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, chenyi.qiang@...el.com,
        shannon.zhao@...ux.alibaba.com,
        Sean Christopherson <seanjc@...gle.com>,
        hao.xiang@...ux.alibaba.com
Subject: Re: [PATCH] KVM: VMX: Check if bus lock vmexit was preempted


On 2021/9/22 20:40, Paolo Bonzini wrote:
> On 22/09/21 12:32, Xiaoyao Li wrote:
>>>
>>
>> EXIT_REASON.bus_lock_detected may or may not be set when exit reason 
>> == EXIT_REASON_BUS_LOCK. Intel will update ISE or SDM to state it.
>>
>> Maybe we can do below in handle_bus_lock_vmexit handler:
>>
>>      if (!to_vmx(vcpu)->exit_reason.bus_lock_detected)
>>          to_vmx(vcpu)->exit_reason.bus_lock_detected = 1;
>>
>> But is manually changing the hardware reported value for software 
>> purpose a good thing?
>
> No.  That said, Hao's patch is just making the code clearer; there's 
> no behavioral change since the "if" will just redo the same 
> assignments as handle_bus_lock_vmexit.
>
> Paolo
I agree Paolo. EXIT_REASON.bus_lock_detected may or may not be set when 
exit_reason=EXIT_REASON_BUS_LOCK,  It clould depend on hardware 
implementaion. No matter when intel states it clearly, I think it is 
better that we avoid repeated assignment by adding additional check 
condition in vmx_handle_exit.  Of course , it is also ok that 
hand_bus_lock_vmexit do nothing , but the code is not clear, and the 
code logic will be inconsistent with spec description.