linux-kernel - Re: [PATCH v15 21/41] KVM: nVMX: Prepare for enabling CET support for nested guest

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Message-ID: <dcab546d-8a9a-42c5-ad7c-3484e505ffba@zytor.com>
Date: Mon, 15 Sep 2025 10:45:59 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Mathias Krause <minipli@...ecurity.net>,
        John Allen <john.allen@....com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Chao Gao <chao.gao@...el.com>, Maxim Levitsky <mlevitsk@...hat.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v15 21/41] KVM: nVMX: Prepare for enabling CET support for
 nested guest

On 9/12/2025 4:22 PM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@...el.com>
> 
> Set up CET MSRs, related VM_ENTRY/EXIT control bits and fixed CR4 setting
> to enable CET for nested VM.
> 
> vmcs12 and vmcs02 needs to be synced when L2 exits to L1 or when L1 wants
> to resume L2, that way correct CET states can be observed by one another.
> 
> Please note that consistency checks regarding CET state during VM-Entry
> will be added later to prevent this patch from becoming too large.
> Advertising the new CET VM_ENTRY/EXIT control bits are also be deferred
> until after the consistency checks are added.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Tested-by: Mathias Krause <minipli@...ecurity.net>
> Tested-by: John Allen <john.allen@....com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>


Reviewed-by: Xin Li (Intel) <xin@...or.com>


> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 14f9822b611d..51d69f368689 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4760,6 +4825,18 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>   	if (vmcs12->vm_exit_controls & VM_EXIT_CLEAR_BNDCFGS)
>   		vmcs_write64(GUEST_BNDCFGS, 0);
>   
> +	/*
> +	 * Load CET state from host state if VM_EXIT_LOAD_CET_STATE is set.
> +	 * otherwise CET state should be retained across VM-exit, i.e.,
> +	 * guest values should be propagated from vmcs12 to vmcs01.
> +	 */
> +	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_CET_STATE)
> +		vmcs_write_cet_state(vcpu, vmcs12->host_s_cet, vmcs12->host_ssp,
> +				     vmcs12->host_ssp_tbl);
> +	else
> +		vmcs_write_cet_state(vcpu, vmcs12->guest_s_cet, vmcs12->guest_ssp,
> +				     vmcs12->guest_ssp_tbl);
> +
>   	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PAT) {
>   		vmcs_write64(GUEST_IA32_PAT, vmcs12->host_ia32_pat);
>   		vcpu->arch.pat = vmcs12->host_ia32_pat;

Also tested with VM exit load CET bit set and cleared, both passed, so

Tested-by: Xin Li (Intel) <xin@...or.com>