Re: How to enable Pause Loop Exiting (PLE)?

["Zhang Haoyu" <zhanghy@sangfor.com>]

>>>>>>Hi,
>>>>>>
>>>>>>I am using this tool for querying VMX capabilities.
>>>>>>
>>>>>>http://git.qemu.org/?p=qemu.git;a=blob_plain;f=scripts/kvm/vmxcap;hb=HEAD
>>>>>>
>>>>>>And it shows as below that pause-loop exiting is not enabled. My kernel is 3.14.
>>>>>>
>>>>>>secondary processor-based controls
>>>>>>  Virtualize APIC accesses                 yes
>>>>>>  Enable EPT                               yes
>>>>>>  Descriptor-table exiting                 yes
>>>>>>  Enable RDTSCP                            yes
>>>>>>  Virtualize x2APIC mode                   yes
>>>>>>  Enable VPID                              yes
>>>>>>  WBINVD exiting                           yes
>>>>>>  Unrestricted guest                       no
>>>>>>  APIC register emulation                  no
>>>>>>  Virtual interrupt delivery               no
>>>>>>  PAUSE-loop exiting                       no
>>>>>>  RDRAND exiting                           no
>>>>>>  Enable INVPCID                           no
>>>>>>  Enable VM functions                      no
>>>>>>  VMCS shadowing                           no
>>>>>>  EPT-violation #VE                        no
>>>>>>
>>>>>>What shall I do if I wish to enable PLE? I have also tried this:
>>>>>>
>>>>> From above info, your physical cpu dose not support ple feature,
>>>>> if you want to enable ple, your cpu must support ple feature, and 'PAUSE exiting' must be 0-settting, 'PAUSE-loop exiting' must be 1-setting.
>>>>> And, kvm-intel module will enable ple as default if your cpu support ple feature.
>>>>>
>>>>Hi, Haoyu,
>>>>
>>>>I have another machine, in which Pause Loop Exiting is showing yes,
>>>>but PAUSE Exiting is also showing yes, see below, but you said PAUSE
>>>>exiting must be 0 setting, so what shall I do? Is PLE enabled or not?
>>>>
>>>check /sys/module/kvm_intel/parameters/ple_gap, if non-zero(>0), ple is enabled, zero means ple is disabled.
>>>
>> Sorry, even /sys/module/kvm_intel/parameters/ple_gap is non-zero, it cannot say ple is enabled, it only means 'PAUSE-loop exiting' is 1-setting,
>> but the 'PAUSE-loop exiting' is ignored if 'PAUSE exiting' is 1-settting.
>> But
>> Below words is from the intel 64 and IA-32 Architectures Software Developer’s Manual Volume 3C,
>> • PAUSE.The behavior of each of this instruction depends on CPL and the settings of the “PAUSE exiting” and
>>   “PAUSE-loop exiting” VM-execution controls:
>>   — CPL= 0.
>>     • If the “PAUSE exiting” and “PAUSE-loop exiting” VM-execution controls are both 0, the PAUSE
>>       instruction executes normally.
>>     • If the “PAUSE exiting” VM-execution control is 1, the PAUSE instruction causes a VM exit (the “PAUSEloop
>>       exiting” VM-execution control is ignored if CPL = 0 and the “PAUSE exiting” VM-execution control
>>       is 1).
>>     • If the “PAUSE exiting” VM-execution control is 0 and the “PAUSE-loop exiting” VM-execution control is
>>       1, the following treatment applies.
>>       The processor determines the amount of time between this execution of PAUSE and the previous
>>       execution of PAUSE at CPL 0. If this amount of time exceeds the value of the VM-execution control field
>>       PLE_Gap, the processor considers this execution to be the first execution of PAUSE in a loop. (It also
>>       does so for the first execution of PAUSE at CPL 0 after VM entry.)
>>       Otherwise, the processor determines the amount of time since the most recent execution of PAUSE that
>>       was considered to be the first in a loop. If this amount of time exceeds the value of the VM-execution
>>       control field PLE_Window, a VM exit occurs.
>>       For purposes of these computations, time is measured based on a counter that runs at the same rate as
>>       the timestamp counter (TSC).
>>   — CPL> 0.
>>     • If the “PAUSE exiting” VM-execution control is 0, the PAUSE instruction executes normally.
>>     • If the “PAUSE exiting” VM-execution control is 1, the PAUSE instruction causes a VM exit.
>>     The “PAUSE-loop exiting” VM-execution control is ignored if CPL > 0.
>>
>Thanks. So PLE is still not enabled on my machine? Then how to let
>"PAUSE Exiting" to be 0-setting?
>
Sorry, I don't know, but you can make a confirmation first.
"PAUSE Exiting" is 0-setting in setup_vmcs_config() function, but it maybe 1-setting in adjust_vmx_controls(),
so you can printk the bitwise-and result of (_cpu_based_exec_control & CPU_BASED_PAUSE_EXITING) after adjust_vmx_controls in setup_vmcs_config.

Any better ideas?

Thanks,
Zhang Haoyu
 
>-Jidong
>
>>>>primary processor-based controls
>>>>  Interrupt window exiting                 yes
>>>>  Use TSC offsetting                       yes
>>>>  HLT exiting                              yes
>>>>  INVLPG exiting                           yes
>>>>  MWAIT exiting                            yes
>>>>  RDPMC exiting                            yes
>>>>  RDTSC exiting                            yes
>>>>  CR3-load exiting                         default
>>>>  CR3-store exiting                        default
>>>>  CR8-load exiting                         yes
>>>>  CR8-store exiting                        yes
>>>>  Use TPR shadow                           yes
>>>>  NMI-window exiting                       yes
>>>>  MOV-DR exiting                           yes
>>>>  Unconditional I/O exiting                yes
>>>>  Use I/O bitmaps                          yes
>>>>  Monitor trap flag                        yes
>>>>  Use MSR bitmaps                          yes
>>>>  MONITOR exiting                          yes
>>>>  PAUSE exiting                            yes
>>>>  Activate secondary control               yes
>>>>secondary processor-based controls
>>>>  Virtualize APIC accesses                 yes
>>>>  Enable EPT                               yes
>>>>  Descriptor-table exiting                 yes
>>>>  Enable RDTSCP                            yes
>>>>  Virtualize x2APIC mode                   yes
>>>>  Enable VPID                              yes
>>>>  WBINVD exiting                           yes
>>>>  Unrestricted guest                       yes
>>>>  APIC register emulation                  no
>>>>  Virtual interrupt delivery               no
>>>>  PAUSE-loop exiting                       yes
>>>>  RDRAND exiting                           no
>>>>  Enable INVPCID                           no
>>>>  Enable VM functions                      no
>>>>  VMCS shadowing                           no
>>>>  EPT-violation #VE                        no