[PATCH v3 6/8] KVM:VMX: Load Guest CET via VMCS when CET is enabled in Guest

[Yang Weijiang]

"Load Guest CET state" bit controls whether guest CET states
will be loaded at Guest entry. Before doing that, KVM needs
to check if CPU CET feature is available.

Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 89ee086e1729..d32cee9ee079 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -55,6 +55,7 @@
 #include <asm/mmu_context.h>
 #include <asm/spec-ctrl.h>
 #include <asm/mshyperv.h>
+#include <asm/cet.h>
 
 #include "trace.h"
 #include "pmu.h"
@@ -4065,6 +4066,20 @@ static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
 	return !(val & ~valid_bits);
 }
 
+static int vmx_guest_cet_cap(struct kvm_vcpu *vcpu)
+{
+	u32 eax, ebx, ecx, edx;
+
+	/*
+	 * Guest CET can work as long as HW supports the feature, independent
+	 * to Host SW enabling status.
+	 */
+	cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
+
+	return ((ecx & bit(X86_FEATURE_SHSTK)) |
+		(edx & bit(X86_FEATURE_IBT))) ? 1 : 0;
+}
+
 static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
 {
 	switch (msr->index) {
@@ -5409,6 +5424,23 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	/*
+	 * To enable Guest CET, check whether CPU CET feature is
+	 * available, if it's there, set Guest CET state loading bit
+	 * per CR4.CET status, otherwise, return a fault to Guest.
+	 */
+	if (vmx_guest_cet_cap(vcpu)) {
+		if (cr4 & X86_CR4_CET) {
+			vmcs_set_bits(VM_ENTRY_CONTROLS,
+				      VM_ENTRY_LOAD_GUEST_CET_STATE);
+		} else {
+			vmcs_clear_bits(VM_ENTRY_CONTROLS,
+					VM_ENTRY_LOAD_GUEST_CET_STATE);
+		}
+	} else if (cr4 & X86_CR4_CET) {
+		return 1;
+	}
+
 	if (to_vmx(vcpu)->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
 		return 1;
 
-- 
2.17.1