hv: PAUSE-loop exiting support in hypervisor

As we enabled cpu sharing, PAUSE-loop exiting can help vcpu
to release its pcpu proactively. It's good for performance.

VMX_PLE_GAP: upper bound on the amount of time between two successive
executions of PAUSE in a loop.
VMX_PLE_WINDOW: upper bound on the amount of time a guest is allowed to
execute in a PAUSE loop

Tracked-On: #4329
Signed-off-by: Shuo A Liu <shuo.a.liu@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/arch/x86/guest/vmcs.c

@@ -297,7 +297,8 @@ static void init_exec_ctrl(struct acrn_vcpu *vcpu)
 	 */
 	value32 = check_vmx_ctrl(MSR_IA32_VMX_PROCBASED_CTLS2,
 			VMX_PROCBASED_CTLS2_VAPIC | VMX_PROCBASED_CTLS2_EPT |VMX_PROCBASED_CTLS2_VPID |
-			VMX_PROCBASED_CTLS2_RDTSCP | VMX_PROCBASED_CTLS2_UNRESTRICT);
+			VMX_PROCBASED_CTLS2_RDTSCP | VMX_PROCBASED_CTLS2_UNRESTRICT |
+			VMX_PROCBASED_CTLS2_PAUSE_LOOP);
 
 	/* SDM Vol3, 25.3,  setting "enable INVPCID" VM-execution to 1 with "INVLPG exiting" disabled,
 	 * passes-through INVPCID instruction to guest if the instruction is supported.
@@ -425,6 +426,10 @@ static void init_exec_ctrl(struct acrn_vcpu *vcpu)
 	exec_vmwrite(VMX_CR3_TARGET_1, 0UL);
 	exec_vmwrite(VMX_CR3_TARGET_2, 0UL);
 	exec_vmwrite(VMX_CR3_TARGET_3, 0UL);
+
+	/* Setup PAUSE-loop exiting - 24.6.13 */
+	exec_vmwrite(VMX_PLE_GAP, 128U);
+	exec_vmwrite(VMX_PLE_WINDOW, 4096U);
 }
 
 static void init_entry_ctrl(const struct acrn_vcpu *vcpu)

hypervisor/arch/x86/guest/vmexit.c

@@ -30,6 +30,7 @@ static int32_t unhandled_vmexit_handler(struct acrn_vcpu *vcpu);
 static int32_t xsetbv_vmexit_handler(struct acrn_vcpu *vcpu);
 static int32_t wbinvd_vmexit_handler(struct acrn_vcpu *vcpu);
 static int32_t undefined_vmexit_handler(struct acrn_vcpu *vcpu);
+static int32_t pause_vmexit_handler(__unused struct acrn_vcpu *vcpu);
 
 /* VM Dispatch table for Exit condition handling */
 static const struct vm_exit_dispatch dispatch_table[NR_VMX_EXIT_REASONS] = {
@@ -113,7 +114,7 @@ static const struct vm_exit_dispatch dispatch_table[NR_VMX_EXIT_REASONS] = {
 	[VMX_EXIT_REASON_MONITOR] = {
 		.handler = unhandled_vmexit_handler},
 	[VMX_EXIT_REASON_PAUSE] = {
-		.handler = unhandled_vmexit_handler},
+		.handler = pause_vmexit_handler},
 	[VMX_EXIT_REASON_ENTRY_FAILURE_MACHINE_CHECK] = {
 		.handler = unhandled_vmexit_handler},
 	[VMX_EXIT_REASON_TPR_BELOW_THRESHOLD] = {
@@ -277,6 +278,12 @@ static int32_t triple_fault_vmexit_handler(struct acrn_vcpu *vcpu)
 	return 0;
 }
 
+static int32_t pause_vmexit_handler(__unused struct acrn_vcpu *vcpu)
+{
+	yield_current();
+	return 0;
+}
+
 int32_t cpuid_vmexit_handler(struct acrn_vcpu *vcpu)
 {
 	uint64_t rax, rbx, rcx, rdx;