[PATCH v6 7/8] kvm: vmx: Enable MSR_TEST_CTRL for intel guest

[Xiaoyao Li]

Only enabling the read and write zero of MSR_TEST_CTRL. This makes
MSR_TEST_CTRL always available for intel guest, but guset cannot write any
value to it except zero.

This matches the truth that most Intel CPUs support MSR_TEST_CTRL, and
it also alleviates the effort to handle wrmsr/rdmsr when exposing split
lock detect to guest in the following patch.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 10 ++++++++++
 arch/x86/kvm/vmx/vmx.h |  1 +
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 300e1e149372..a302027f7e56 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1820,6 +1820,9 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	u32 index;
 
 	switch (msr_info->index) {
+	case MSR_TEST_CTRL:
+		msr_info->data = vmx->msr_test_ctrl;
+		break;
 #ifdef CONFIG_X86_64
 	case MSR_FS_BASE:
 		msr_info->data = vmcs_readl(GUEST_FS_BASE);
@@ -1973,6 +1976,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	u32 index;
 
 	switch (msr_index) {
+	case MSR_TEST_CTRL:
+		if (data)
+			return 1;
+
+		vmx->msr_test_ctrl = data;
+		break;
 	case MSR_EFER:
 		ret = kvm_set_msr_common(vcpu, msr_info);
 		break;
@@ -4283,6 +4292,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
+	vmx->msr_test_ctrl = 0;
 
 	vmx->msr_ia32_umwait_control = 0;
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index be93d597306c..7ef9cc085188 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -224,6 +224,7 @@ struct vcpu_vmx {
 #endif
 
 	u64		      spec_ctrl;
+	u64		      msr_test_ctrl;
 	u32		      msr_ia32_umwait_control;
 
 	u32 secondary_exec_control;
-- 
2.20.1