linux-kernel - Re: [PATCH v6 8/8] kvm: vmx: virtualize split lock detection

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Date:   Thu, 26 Mar 2020 14:41:14 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v6 8/8] kvm: vmx: virtualize split lock detection

On 3/25/2020 8:40 AM, Thomas Gleixner wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>> +static inline bool guest_cpu_split_lock_detect_on(struct vcpu_vmx *vmx)
>> +{
>> +	return vmx->msr_test_ctrl & MSR_TEST_CTRL_SPLIT_LOCK_DETECT;
>> +}
>> +
>>   static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>>   {
>>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> @@ -4725,12 +4746,13 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>>   	case AC_VECTOR:
>>   		/*
>>   		 * Reflect #AC to the guest if it's expecting the #AC, i.e. has
>> -		 * legacy alignment check enabled.  Pre-check host split lock
>> -		 * support to avoid the VMREADs needed to check legacy #AC,
>> -		 * i.e. reflect the #AC if the only possible source is legacy
>> -		 * alignment checks.
>> +		 * legacy alignment check enabled or split lock detect enabled.
>> +		 * Pre-check host split lock support to avoid further check of
>> +		 * guest, i.e. reflect the #AC if host doesn't enable split lock
>> +		 * detection.
>>   		 */
>>   		if (!split_lock_detect_on() ||
>> +		    guest_cpu_split_lock_detect_on(vmx) ||
>>   		    guest_cpu_alignment_check_enabled(vcpu)) {
> 
> If the host has split lock detection disabled then how is the guest
> supposed to have it enabled in the first place?
> 

It is ||

Thanks,
-Xiaoyao