Re: [Xen-devel] [PATCH RFC V2 3/6] xen: Force-enable relevant MSR events; optimize the number of sent MSR events

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

>>> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c
>>> b/xen/arch/x86/hvm/vmx/vmcs.c index 8ffc562..35fcfcc 100644
>>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>>> @@ -700,6 +700,24 @@ void vmx_disable_intercept_for_msr(struct vcpu
>*v, u32 msr, int type)
>>>      if ( msr_bitmap == NULL )
>>>          return;
>>>
>>> +    /* Filter out MSR-s needed for memory introspection */
>>> +    switch ( msr )
>>
>> This absolutely must be gated on mem_events being enabled for the
>domain.
>>
>> It is too much of a performance penalty to apply to domains which are
>> not being introspected.
>
>I understand, but it really runs very early on, and the mem_event part comes
>in after the MSR interception is disabled. This effectively renders a lot of
>memory introspection functionality useless.

How about using a Xen command line parameter and gate it based on that rather 
than a mem_event listener being present? 

Thanks,
Aravindh

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