Re: [RFC PATCH 16/18] KVM: add kvm_arch_vcpu_prevent_run to prevent VM ENTER when NMI is received

[Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>]

On 2012/06/29 1:48, Avi Kivity wrote:
> On 06/28/2012 09:08 AM, Tomoki Sekiyama wrote:
>> Since NMI can not be disabled around VM enter, there is a race between
>> receiving NMI to kick a guest and entering the guests on slave CPUs.If the
>> NMI is received just before entering VM, after the NMI handler is invoked,
>> it continues entering the guest and the effect of the NMI will be lost.
>>
>> This patch adds kvm_arch_vcpu_prevent_run(), which causes VM exit right
>> after VM enter. The NMI handler uses this to ensure the execution of the
>> guest is cancelled after NMI.
>>
>>  
>> +/*
>> + * Make VMRESUME fail using preemption timer with timer value = 0.
>> + * On processors that doesn't support preemption timer, VMRESUME will fail
>> + * by internal error.
>> + */
>> +static void vmx_prevent_run(struct kvm_vcpu *vcpu, int prevent)
>> +{
>> +	if (prevent)
>> +		vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL,
>> +			      PIN_BASED_PREEMPTION_TIMER);
>> +	else
>> +		vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
>> +				PIN_BASED_PREEMPTION_TIMER);
>> +}
> 
> This may interrupt another RMW sequence, which will then overwrite the
> control.  So it needs to be called only if inside the entry sequence
> (otherwise can just set a KVM_REQ_IMMEDIATE_EXIT in vcpu->requests).
> 

I agree. I will add the check whether it is in the entry sequence.

Thanks,
-- 
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory