[PATCH v16 34/51] KVM: nVMX: Advertise new VM-Entry/Exit control bits for CET state

Sean Christopherson
2025-09-19T22:34:07Z

From: Chao Gao <chao.gao@intel.com>

Advertise the LOAD_CET_STATE VM-Entry/Exit control bits in the nested VMX
MSRS, as all nested support for CET virtualization, including consistency
checks, is in place.

Advertise support if and only if KVM supports at least one of IBT or SHSTK.
While it's userspace's responsibility to provide a consistent CPU model to
the guest, that doesn't mean KVM should set userspace up to fail.

Note, the existing {CLEAR,LOAD}_BNDCFGS behavior predates
KVM_X86_QUIRK_STUFF_FEATURE_MSRS, i.e. KVM "solved" the inconsistent CPU
model problem by overwriting the VMX MSRs provided by userspace.

Signed-off-by: Chao Gao <chao.gao@intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/nested.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 024bfb4d3a72..a8a421a8e766 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -7178,13 +7178,17 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf,
VM_EXIT_HOST_ADDR_SPACE_SIZE |
#endif
VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |
- VM_EXIT_CLEAR_BNDCFGS;
+ VM_EXIT_CLEAR_BNDCFGS | VM_EXIT_LOAD_CET_STATE;
msrs->exit_ctls_high |=
VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER |
VM_EXIT_SAVE_VMX_PREEMPTION_TIMER | VM_EXIT_ACK_INTR_ON_EXIT |
VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;

+ if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
+ !kvm_cpu_cap_has(X86_FEATURE_IBT))
+ msrs->exit_ctls_high &= ~VM_EXIT_LOAD_CET_STATE;
+
/* We support free control of debug control saving. */
msrs->exit_ctls_low &= ~VM_EXIT_SAVE_DEBUG_CONTROLS;
}
@@ -7200,11 +7204,16 @@ static void nested_vmx_setup_entry_ctls(struct vmcs_config *vmcs_conf,
#ifdef CONFIG_X86_64
VM_ENTRY_IA32E_MODE |
#endif
- VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS;
+ VM_ENTRY_LOAD_IA32_PAT | VM_ENTRY_LOAD_BNDCFGS |
+ VM_ENTRY_LOAD_CET_STATE;
msrs->entry_ctls_high |=
(VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR | VM_ENTRY_LOAD_IA32_EFER |
VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);

+ if (!kvm_cpu_cap_has(X86_FEATURE_SHSTK) &&
+ !kvm_cpu_cap_has(X86_FEATURE_IBT))
+ msrs->exit_ctls_high &= ~VM_ENTRY_LOAD_CET_STATE;
+
/* We support free control of debug control loading. */
msrs->entry_ctls_low &= ~VM_ENTRY_LOAD_DEBUG_CONTROLS;
}
--
2.51.0.470.ga7dc726c21-goog