[PATCH v2] KVM: nVMX: Fully support of nested VMX preemption timer

[Arthur Chunqi Li <yzt356@gmail.com>]

This patch contains the following two changes:
1. Fix the bug in nested preemption timer support. If vmexit L2->L0
with some reasons not emulated by L1, preemption timer value should
be save in such exits.
2. Add support of "Save VMX-preemption timer value" VM-Exit controls
to nVMX.

With this patch, nested VMX preemption timer features are fully
supported.

Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
---
 arch/x86/kvm/vmx.c |   49 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 57b4e12..6aa320e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2204,7 +2204,14 @@ static __init void nested_vmx_setup_ctls_msrs(void)
 #ifdef CONFIG_X86_64
 		VM_EXIT_HOST_ADDR_SPACE_SIZE |
 #endif
-		VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT;
+		VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |
+		VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
+	if (!(nested_vmx_pinbased_ctls_high & PIN_BASED_VMX_PREEMPTION_TIMER))
+		nested_vmx_exit_ctls_high &=
+			(~VM_EXIT_SAVE_VMX_PREEMPTION_TIMER);
+	if (!(nested_vmx_exit_ctls_high & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER))
+		nested_vmx_pinbased_ctls_high &=
+			(~PIN_BASED_VMX_PREEMPTION_TIMER);
 	nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
 				      VM_EXIT_LOAD_IA32_EFER);
 
@@ -6706,6 +6713,22 @@ static void vmx_get_exit_info(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2)
 	*info2 = vmcs_read32(VM_EXIT_INTR_INFO);
 }
 
+static void nested_fix_preempt(struct kvm_vcpu *vcpu)
+{
+	u64 delta_guest_tsc;
+	u32 preempt_val, preempt_bit, delta_preempt_val;
+
+	preempt_bit = native_read_msr(MSR_IA32_VMX_MISC) & 0x1F;
+	delta_guest_tsc = kvm_x86_ops->read_l1_tsc(vcpu,
+			native_read_tsc()) - vcpu->arch.last_guest_tsc;
+	delta_preempt_val = delta_guest_tsc >> preempt_bit;
+	preempt_val = vmcs_read32(VMX_PREEMPTION_TIMER_VALUE);
+	if (preempt_val - delta_preempt_val < 0)
+		preempt_val = 0;
+	else
+		preempt_val -= delta_preempt_val;
+	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, preempt_val);
+}
 /*
  * The guest has exited.  See if we can fix it or if we need userspace
  * assistance.
@@ -6734,9 +6757,12 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 	else
 		vmx->nested.nested_run_pending = 0;
 
-	if (is_guest_mode(vcpu) && nested_vmx_exit_handled(vcpu)) {
-		nested_vmx_vmexit(vcpu);
-		return 1;
+	if (is_guest_mode(vcpu)) {
+		if (nested_vmx_exit_handled(vcpu)) {
+			nested_vmx_vmexit(vcpu);
+			return 1;
+		} else
+			nested_fix_preempt(vcpu);
 	}
 
 	if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
@@ -7517,6 +7543,7 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 exec_control;
+	u32 exit_control;
 
 	vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
 	vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
@@ -7690,7 +7717,10 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	 * we should use its exit controls. Note that VM_EXIT_LOAD_IA32_EFER
 	 * bits are further modified by vmx_set_efer() below.
 	 */
-	vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
+	exit_control = vmcs_config.vmexit_ctrl;
+	if (vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER)
+		exit_control |= VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
+	vmcs_write32(VM_EXIT_CONTROLS, exit_control);
 
 	/* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
 	 * emulated by vmx_set_efer(), below.
@@ -8089,6 +8119,15 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	vmcs12->guest_pending_dbg_exceptions =
 		vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS);
 
+	if (vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER) {
+		if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
+			vmcs12->vmx_preemption_timer_value =
+				vmcs_read32(VMX_PREEMPTION_TIMER_VALUE);
+		else
+			vmcs_write32(VMX_PREEMPTION_TIMER_VALUE,
+					vmcs12->vmx_preemption_timer_value);
+	}
+
 	/*
 	 * In some cases (usually, nested EPT), L2 is allowed to change its
 	 * own CR3 without exiting. If it has changed it, we must keep it.
-- 
1.7.9.5