KVM: VMX: Add support for Pause-Loop Exiting
New NHM processors will support Pause-Loop Exiting by adding 2 VM-execution
control fields:
PLE_Gap - upper bound on the amount of time between two successive
executions of PAUSE in a loop.
PLE_Window - upper bound on the amount of time a guest is allowed to execute in
a PAUSE loop
If the time, between this execution of PAUSE and previous one, exceeds the
PLE_Gap, processor consider this PAUSE belongs to a new loop.
Otherwise, processor determins the the total execution time of this loop(since
1st PAUSE in this loop), and triggers a VM exit if total time exceeds the
PLE_Window.
* Refer SDM volume 3b section 21.6.13 & 22.1.3.
Pause-Loop Exiting can be used to detect Lock-Holder Preemption, where one VP
is sched-out after hold a spinlock, then other VPs for same lock are sched-in
to waste the CPU time.
Our tests indicate that most spinlocks are held for less than 212 cycles.
Performance tests show that with 2X LP over-commitment we can get +2% perf
improvement for kernel build(Even more perf gain with more LPs).
Signed-off-by: Zhai Edwin <edwin.zhai@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index 272514c..2b49454 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -56,6 +56,7 @@
#define SECONDARY_EXEC_ENABLE_VPID 0x00000020
#define SECONDARY_EXEC_WBINVD_EXITING 0x00000040
#define SECONDARY_EXEC_UNRESTRICTED_GUEST 0x00000080
+#define SECONDARY_EXEC_PAUSE_LOOP_EXITING 0x00000400
#define PIN_BASED_EXT_INTR_MASK 0x00000001
@@ -144,6 +145,8 @@
VM_ENTRY_INSTRUCTION_LEN = 0x0000401a,
TPR_THRESHOLD = 0x0000401c,
SECONDARY_VM_EXEC_CONTROL = 0x0000401e,
+ PLE_GAP = 0x00004020,
+ PLE_WINDOW = 0x00004022,
VM_INSTRUCTION_ERROR = 0x00004400,
VM_EXIT_REASON = 0x00004402,
VM_EXIT_INTR_INFO = 0x00004404,
@@ -248,6 +251,7 @@
#define EXIT_REASON_MSR_READ 31
#define EXIT_REASON_MSR_WRITE 32
#define EXIT_REASON_MWAIT_INSTRUCTION 36
+#define EXIT_REASON_PAUSE_INSTRUCTION 40
#define EXIT_REASON_MCE_DURING_VMENTRY 41
#define EXIT_REASON_TPR_BELOW_THRESHOLD 43
#define EXIT_REASON_APIC_ACCESS 44