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Subject[PATCH v6 4/8] KVM: VMX: Pass through CET related MSRs to Guest
CET MSRs pass through Guest directly to enhance performance.
CET runtime control settings are stored in MSR_IA32_{U,S}_CET,
Shadow Stack Pointer(SSP) are stored in MSR_IA32_PL{0,1,2,3}_SSP,
SSP table base address is stored in MSR_IA32_INT_SSP_TAB,
these MSRs are defined in kernel and re-used here.

MSR_IA32_U_CET and MSR_IA32_PL3_SSP are used for user mode protection,
the contents could differ from process to process, therefore,
kernel needs to save/restore them during context switch, it makes
sense to pass through them so that the guest kernel can
use xsaves/xrstors to operate them efficiently. Other MSRs are used
for non-user mode protection. See CET spec for detailed info.

The difference between CET VMCS state fields and xsave components is that,
the former used for CET state storage during VMEnter/VMExit,
whereas the latter used for state retention between Guest task/process

Co-developed-by: Zhang Yi Z <>
Signed-off-by: Zhang Yi Z <>
Signed-off-by: Yang Weijiang <>
arch/x86/kvm/vmx/vmx.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ce1d6fe21780..ce5d1e45b7a5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6952,6 +6952,7 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ unsigned long *msr_bitmap;

if (cpu_has_secondary_exec_ctrls()) {
@@ -6973,6 +6974,19 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
if (boot_cpu_has(X86_FEATURE_INTEL_PT) &&
guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT))
+ msr_bitmap = vmx->vmcs01.msr_bitmap;
+ if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+ guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW);
+ vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW);
+ }

static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
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