[Xen-devel] [Question] About the behavior of HLT in VMX guest mode

["Longpeng (Mike)" <longpeng2@xxxxxxxxxx>]

Hi guys,

I'm confusing about the behavior of HLT instruction in VMX guest mode.

I set "hlt exiting" bit to 0 in VMCS, and the vcpu didn't vmexit when execute
HLT as expected. However, I used powertop/cpupower on host to watch the pcpu's
c-states, it seems that the pcpu didn't enter C1/C1E state during this period.

I searched the Intel spec vol-3, and only found that guest MWAIT won't entering
a low-power sleep state under certain conditions(ch 25.3), but not mentioned 
HLT.

My questions are
1) Does executing HLT instruction in guest-mode won't enter C1/C1E state ?
2) If it won't, then whether it would release the hardware resources shared with
another hyper-thread ?

Any suggestion would be greatly appreciated, thanks!

-- 
Regards,
Longpeng(Mike)


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