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Re: [Xen-devel] [PATCH RFC V5 3/5] xen: Force-enable relevant MSR events; optimize the number of sent MSR events


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
  • Date: Mon, 11 Aug 2014 11:57:36 +0300
  • Cc: kevin.tian@xxxxxxxxx, ian.campbell@xxxxxxxxxx, stefano.stabellini@xxxxxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, eddie.dong@xxxxxxxxx, xen-devel@xxxxxxxxxxxxx, jun.nakajima@xxxxxxxxx, ian.jackson@xxxxxxxxxxxxx
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On 08/08/2014 05:34 PM, Jan Beulich wrote:
>>>> On 06.08.14 at 17:58, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/mm/mem_event.c
>> +++ b/xen/arch/x86/mm/mem_event.c
>> @@ -600,6 +600,9 @@ int mem_event_domctl(struct domain *d, 
>> xen_domctl_mem_event_op_t *mec,
>>              rc = mem_event_enable(d, mec, med, _VPF_mem_access, 
>>                                      HVM_PARAM_ACCESS_RING_PFN,
>>                                      mem_access_notification);
>> +
>> +            if ( rc == 0 && hvm_funcs.enable_intro_msr_interception )
>> +                hvm_funcs.enable_intro_msr_interception(d);
> 
> Isn't the sequence of operations wrong here (leaving a window in
> time where mem events are already enabled but the necessary MSRs
> aren't being intercepted yet? Or was it that guests are being paused
> while all this takes place?

I've looked into how this is implemented on the libxc side, and it would
appear that xc_mem_event_enable() (in xc_mem_event.c) does explicitly
pause the domain before calling xc_mem_event_control() (which ends up in
the code above), so it should not be a problem.


Thanks,
Razvan Cojocaru

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