Re: [PATCH v9 18/22] KVM: nVMX: Enable support for secondary VM exit controls

[Chao Gao <chao.gao@intel.com>]

On Sun, Oct 26, 2025 at 01:19:06PM -0700, Xin Li (Intel) wrote:
>From: Xin Li <xin3.li@intel.com>
>
>Add support for secondary VM exit controls in nested VMX to facilitate
>future FRED integration.
>
>Signed-off-by: Xin Li <xin3.li@intel.com>
>Signed-off-by: Xin Li (Intel) <xin@zytor.com>
>Tested-by: Shan Kang <shan.kang@intel.com>
>Tested-by: Xuelian Guo <xuelian.guo@intel.com>
>---
>
>Changes in v8:
>* Relocate secondary_vm_exit_controls to the last u64 padding field.
>* Remove the change to Documentation/virt/kvm/x86/nested-vmx.rst.
>
>Changes in v5:
>* Allow writing MSR_IA32_VMX_EXIT_CTLS2 (Sean).
>* Add TB from Xuelian Guo.
>
>Change in v3:
>* Read secondary VM exit controls from vmcs_conf insteasd of the hardware
>  MSR MSR_IA32_VMX_EXIT_CTLS2 to avoid advertising features to L1 that KVM
>  itself doesn't support, e.g. because the expected entry+exit pairs aren't
>  supported. (Sean Christopherson)
>---
> arch/x86/kvm/vmx/capabilities.h |  1 +
> arch/x86/kvm/vmx/nested.c       | 26 +++++++++++++++++++++++++-
> arch/x86/kvm/vmx/vmcs12.c       |  1 +
> arch/x86/kvm/vmx/vmcs12.h       |  3 ++-
> arch/x86/kvm/x86.h              |  2 +-
> 5 files changed, 30 insertions(+), 3 deletions(-)
>
>diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
>index 651507627ef3..f390f9f883c3 100644
>--- a/arch/x86/kvm/vmx/capabilities.h
>+++ b/arch/x86/kvm/vmx/capabilities.h
>@@ -34,6 +34,7 @@ struct nested_vmx_msrs {
> 	u32 pinbased_ctls_high;
> 	u32 exit_ctls_low;
> 	u32 exit_ctls_high;
>+	u64 secondary_exit_ctls;
> 	u32 entry_ctls_low;
> 	u32 entry_ctls_high;
> 	u32 misc_low;
>diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>index b0cd745518b4..cbb682424a5b 100644
>--- a/arch/x86/kvm/vmx/nested.c
>+++ b/arch/x86/kvm/vmx/nested.c
>@@ -1534,6 +1534,11 @@ int vmx_set_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
> 			return -EINVAL;
> 		vmx->nested.msrs.vmfunc_controls = data;
> 		return 0;
>+	case MSR_IA32_VMX_EXIT_CTLS2:
>+		if (data & ~vmcs_config.nested.secondary_exit_ctls)
>+			return -EINVAL;
>+		vmx->nested.msrs.secondary_exit_ctls = data;
>+		return 0;
> 	default:
> 		/*
> 		 * The rest of the VMX capability MSRs do not support restore.
>@@ -1573,6 +1578,9 @@ int vmx_get_vmx_msr(struct nested_vmx_msrs *msrs, u32 msr_index, u64 *pdata)
> 		if (msr_index == MSR_IA32_VMX_EXIT_CTLS)
> 			*pdata |= VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
> 		break;
>+	case MSR_IA32_VMX_EXIT_CTLS2:
>+		*pdata = msrs->secondary_exit_ctls;

MSR_IA32_VMX_EXIT_CTLS2 should be added to emulated_msrs_all[] for live migration.