[RFC PATCH v4 5/8] 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 | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 28b8ac027bd7..246467c12930 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"
@@ -5414,6 +5415,23 @@ 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 (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+	    guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
+		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