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Subject: Re: [PATCH v5 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
To:     Xiaoyao Li <xiaoyao.li@linux.intel.com>,
        Tao Xu <tao3.xu@intel.com>, rkrcmar@redhat.com, corbet@lwn.net,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        sean.j.christopherson@intel.com
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        fenghua.yu@intel.com, jingqi.liu@intel.com
References: <20190620084620.17974-1-tao3.xu@intel.com>
 <20190620084620.17974-3-tao3.xu@intel.com>
 <b2cfa1d015315c74af6cee1c00185e5c68cfa397.camel@linux.intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <22533924-f7e8-4b50-d5fe-7cbcc9295b53@redhat.com>
Date:   Tue, 2 Jul 2019 18:37:51 +0200
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On 20/06/19 11:46, Xiaoyao Li wrote:
> You cannot put the atomic switch here. What if umwait_control_cached is changed
> at runtime? Host kernel patch exposed a sysfs interface to let it happen.

Thanks for the review, Xiaoyao.  I agree with both of your remarks.

Paolo

>> +		break;
>>  	case MSR_IA32_SPEC_CTRL:
>>  		if (!msr_info->host_initiated &&
>>  		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
>> @@ -4126,6 +4148,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool
>> init_event)
>>  	vmx->rmode.vm86_active = 0;
>>  	vmx->spec_ctrl = 0;
>>  
>> +	vmx->msr_ia32_umwait_control = 0;
>> +
>>  	vcpu->arch.microcode_version = 0x100000000ULL;
>>  	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
>>  	kvm_set_cr8(vcpu, 0);
>> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
>> index 61128b48c503..8485bec7c38a 100644
>> --- a/arch/x86/kvm/vmx/vmx.h
>> +++ b/arch/x86/kvm/vmx/vmx.h
>> @@ -14,6 +14,8 @@
>>  extern const u32 vmx_msr_index[];
>>  extern u64 host_efer;
>>  
>> +extern u32 umwait_control_cached;
>> +
>>  #define MSR_TYPE_R	1
>>  #define MSR_TYPE_W	2
>>  #define MSR_TYPE_RW	3
>> @@ -194,6 +196,7 @@ struct vcpu_vmx {
>>  #endif
>>  
>>  	u64		      spec_ctrl;
>> +	u64		      msr_ia32_umwait_control;
>>  
>>  	u32 vm_entry_controls_shadow;
>>  	u32 vm_exit_controls_shadow;
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 83aefd759846..4480de459bf4 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1138,6 +1138,7 @@ static u32 msrs_to_save[] = {
>>  	MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
>>  	MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
>>  	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
>> +	MSR_IA32_UMWAIT_CONTROL,
>>  };
>>  
>>  static unsigned num_msrs_to_save;
>