KVM: nVMX: keep preemption timer enabled during L2 execution

Because the vmcs12 preemption timer is emulated through a separate hrtimer,
we can keep on using the preemption timer in the vmcs02 to emulare L1's
TSC deadline timer.

However, the corresponding bit in the pin-based execution control field
must be kept consistent between vmcs01 and vmcs02.  On vmentry we copy
it into the vmcs02; on vmexit the preemption timer must be disabled in
the vmcs01 if a preemption timer vmexit happened while in guest mode.

The preemption timer value in the vmcs02 is set by vmx_vcpu_run, so it
need not be considered in prepare_vmcs02.

Cc: Yunhong Jiang <yunhong.jiang@intel.com>
Cc: Haozhong Zhang <haozhong.zhang@intel.com>
Tested-by: Wanpeng Li <kernellwp@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx.c

@@ -9796,9 +9796,14 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	vmcs_write64(VMCS_LINK_POINTER, -1ull);
 
 	exec_control = vmcs12->pin_based_vm_exec_control;
+
+	/* Preemption timer setting is only taken from vmcs01.  */
+	exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
 	exec_control |= vmcs_config.pin_based_exec_ctrl;
+	if (vmx->hv_deadline_tsc == -1)
 		exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
 
+	/* Posted interrupts setting is only taken from vmcs12.  */
 	if (nested_cpu_has_posted_intr(vmcs12)) {
 		/*
 		 * Note that we use L0's vector here and in
@@ -10727,8 +10732,14 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 
 	load_vmcs12_host_state(vcpu, vmcs12);
 
-	/* Update TSC_OFFSET if TSC was changed while L2 ran */
+	/* Update any VMCS fields that might have changed while L2 ran */
 	vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
+	if (vmx->hv_deadline_tsc == -1)
+		vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
+				PIN_BASED_VMX_PREEMPTION_TIMER);
+	else
+		vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL,
+			      PIN_BASED_VMX_PREEMPTION_TIMER);
 
 	/* This is needed for same reason as it was needed in prepare_vmcs02 */
 	vmx->host_rsp = 0;