===================================================================
@@ -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 @@ enum vmcs_field {
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 @@ enum vmcs_field {
#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
===================================================================
@@ -61,6 +61,25 @@ module_param_named(unrestricted_guest,
static int __read_mostly emulate_invalid_guest_state = 0;
module_param(emulate_invalid_guest_state, bool, S_IRUGO);
+/*
+ * These 2 parameters are used to config the controls for Pause-Loop Exiting:
+ * ple_gap: upper bound on the amount of time between two successive
+ * executions of PAUSE in a loop. Also indicate if ple enabled.
+ * According to test, this time is usually small than 41 cycles.
+ * ple_window: upper bound on the amount of time a guest is allowed to execute
+ * in a PAUSE loop. Tests indicate that most spinlocks are held for
+ * less than 2^12 cycles
+ * Time is measured based on a counter that runs at the same rate as the TSC,
+ * refer SDM volume 3b section 21.6.13 & 22.1.3.
+ */
+#define KVM_VMX_DEFAULT_PLE_GAP 41
+#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
+static int __read_mostly ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
+module_param(ple_gap, int, S_IRUGO);
+
+static int __read_mostly ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
+module_param(ple_window, int, S_IRUGO);
+
struct vmcs {
u32 revision_id;
u32 abort;
@@ -320,6 +339,12 @@ static inline int cpu_has_vmx_unrestrict
SECONDARY_EXEC_UNRESTRICTED_GUEST;
}
+static inline int cpu_has_vmx_ple(void)
+{
+ return vmcs_config.cpu_based_2nd_exec_ctrl &
+ SECONDARY_EXEC_PAUSE_LOOP_EXITING;
+}
+
static inline int vm_need_virtualize_apic_accesses(struct kvm *kvm)
{
return flexpriority_enabled &&
@@ -1240,7 +1265,8 @@ static __init int setup_vmcs_config(stru
SECONDARY_EXEC_WBINVD_EXITING |
SECONDARY_EXEC_ENABLE_VPID |
SECONDARY_EXEC_ENABLE_EPT |
- SECONDARY_EXEC_UNRESTRICTED_GUEST;
+ SECONDARY_EXEC_UNRESTRICTED_GUEST |
+ SECONDARY_EXEC_PAUSE_LOOP_EXITING;
if (adjust_vmx_controls(min2, opt2,
MSR_IA32_VMX_PROCBASED_CTLS2,
&_cpu_based_2nd_exec_control) < 0)
@@ -1387,6 +1413,9 @@ static __init int hardware_setup(void)
if (enable_ept && !cpu_has_vmx_ept_2m_page())
kvm_disable_largepages();
+ if (!cpu_has_vmx_ple())
+ ple_gap = 0;
+
return alloc_kvm_area();
}
@@ -2301,9 +2330,16 @@ static int vmx_vcpu_setup(struct vcpu_vm
exec_control &= ~SECONDARY_EXEC_ENABLE_EPT;
if (!enable_unrestricted_guest)
exec_control &= ~SECONDARY_EXEC_UNRESTRICTED_GUEST;
+ if (!ple_gap)
+ exec_control &= ~SECONDARY_EXEC_PAUSE_LOOP_EXITING;
vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
}
+ if (ple_gap) {
+ vmcs_write32(PLE_GAP, ple_gap);
+ vmcs_write32(PLE_WINDOW, ple_window);
+ }
+
vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, !!bypass_guest_pf);
vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, !!bypass_guest_pf);
vmcs_write32(CR3_TARGET_COUNT, 0); /* 22.2.1 */
@@ -3351,6 +3387,18 @@ static void handle_invalid_guest_state(s
}
/*
+ * Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
+ * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
+ */
+static int handle_pause(struct kvm_vcpu *vcpu,
+ struct kvm_run *kvm_run)
+{
+ skip_emulated_instruction(vcpu);
+ yield();
+ return 1;
+}
+
+/*
* The exit handlers return 1 if the exit was handled fully and guest execution
* may resume. Otherwise they set the kvm_run parameter to indicate what needs
* to be done to userspace and return 0.
@@ -3387,6 +3435,7 @@ static int (*kvm_vmx_exit_handlers[])(st
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
+ [EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
};
static const int kvm_vmx_max_exit_handlers =
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 2^12 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> ---- include/asm/vmx.h | 4 ++++ kvm/vmx.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 54 insertions(+), 1 deletion(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html