[PATCH v6 12/20] kvm/vmx: Emulate MSR TEST_CTL

[Fenghua Yu]

From: Xiaoyao Li <xiaoyao.li@xxxxxxxxxxxxxxx>

A control bit (bit 29) in TEST_CTL MSR 0x33 will be introduced in
future x86 processors. When bit 29 is set, the processor causes #AC
exception for split locked accesses at all CPL.

Please check the latest Intel 64 and IA-32 Architectures Software
Developer's Manual for more detailed information on the MSR and
the split lock bit.

This patch emulate MSR TEST_CTL with vmx->msr_test_ctl and does the
following:
1. As MSR TEST_CTL of guest is emulated, enable the related bits
in CORE_CAPABILITY to corretly report this feature to guest.

2. Differentiate MSR TEST_CTL between host and guest.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 35 +++++++++++++++++++++++++++++++++++
 arch/x86/kvm/vmx/vmx.h |  1 +
 arch/x86/kvm/x86.c     | 17 ++++++++++++++++-
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ab432a930ae8..309ccf593f0d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1663,6 +1663,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	u32 index;
 
 	switch (msr_info->index) {
+	case MSR_TEST_CTL:
+		if (!msr_info->host_initiated &&
+		    !(vcpu->arch.core_capability & CORE_CAP_SPLIT_LOCK_DETECT))
+			return 1;
+		msr_info->data = vmx->msr_test_ctl;
+		break;
 #ifdef CONFIG_X86_64
 	case MSR_FS_BASE:
 		msr_info->data = vmcs_readl(GUEST_FS_BASE);
@@ -1797,6 +1803,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	u32 index;
 
 	switch (msr_index) {
+	case MSR_TEST_CTL:
+		if (!(vcpu->arch.core_capability & CORE_CAP_SPLIT_LOCK_DETECT))
+			return 1;
+
+		if (data & ~TEST_CTL_ENABLE_SPLIT_LOCK_DETECT)
+			return 1;
+		vmx->msr_test_ctl = data;
+		break;
 	case MSR_EFER:
 		ret = kvm_set_msr_common(vcpu, msr_info);
 		break;
@@ -4077,6 +4091,9 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
 		++vmx->nmsrs;
 	}
 
+	/* disable AC split lock by default */
+	vmx->msr_test_ctl = 0;
+
 	vm_exit_controls_init(vmx, vmx_vmexit_ctrl());
 
 	/* 22.2.1, 20.8.1 */
@@ -4114,6 +4131,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
+	vmx->msr_test_ctl = 0;
 
 	vcpu->arch.microcode_version = 0x100000000ULL;
 	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
@@ -6313,6 +6331,21 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
 					msrs[i].host, false);
 }
 
+static void atomic_switch_msr_test_ctl(struct vcpu_vmx *vmx)
+{
+	u64 host_msr_test_ctl;
+
+	/* if TEST_CTL MSR doesn't exist on the hardware, do nothing */
+	if (rdmsrl_safe(MSR_TEST_CTL, &host_msr_test_ctl))
+		return;
+
+	if (host_msr_test_ctl == vmx->msr_test_ctl)
+		clear_atomic_switch_msr(vmx, MSR_TEST_CTL);
+	else
+		add_atomic_switch_msr(vmx, MSR_TEST_CTL, vmx->msr_test_ctl,
+				      host_msr_test_ctl, false);
+}
+
 static void vmx_arm_hv_timer(struct vcpu_vmx *vmx, u32 val)
 {
 	vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, val);
@@ -6419,6 +6452,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 
 	atomic_switch_perf_msrs(vmx);
 
+	atomic_switch_msr_test_ctl(vmx);
+
 	vmx_update_hv_timer(vcpu);
 
 	/*
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index a1e00d0a2482..6091a8b9de74 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -190,6 +190,7 @@ struct vcpu_vmx {
 	u64		      msr_guest_kernel_gs_base;
 #endif
 
+	u64		      msr_test_ctl;
 	u64		      spec_ctrl;
 
 	u32 vm_entry_controls_shadow;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4459115eb0ec..e93c2f620cdb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1229,7 +1229,22 @@ EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
 
 u64 kvm_get_core_capability(void)
 {
-	return 0;
+	u64 data;
+
+	rdmsrl_safe(MSR_IA32_CORE_CAPABILITY, &data);
+
+	/* mask non-virtualizable functions */
+	data &= CORE_CAP_SPLIT_LOCK_DETECT;
+
+	/*
+	 * There will be a list of FMS values that have split lock detection
+	 * but lack the CORE CAPABILITY MSR. In this case, set
+	 * CORE_CAP_SPLIT_LOCK_DETECT since we emulate MSR CORE_CAPABILITY.
+	 */
+	if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
+		data |= CORE_CAP_SPLIT_LOCK_DETECT;
+
+	return data;
 }
 EXPORT_SYMBOL_GPL(kvm_get_core_capability);
 
-- 
2.19.1