linux-kernel - Re: [PATCH v9 10/22] KVM: VMX: Add support for saving and restoring FRED MSRs

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Message-Id: <1D26E0E9-5826-4443-AB99-8620AC901BE2@zytor.com>
Date: Sun, 30 Nov 2025 22:20:28 -0800
From: Xin Li <xin@...or.com>
To: Chao Gao <chao.gao@...el.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        luto@...nel.org, peterz@...radead.org, andrew.cooper3@...rix.com,
        hch@...radead.org, sohil.mehta@...el.com
Subject: Re: [PATCH v9 10/22] KVM: VMX: Add support for saving and restoring
 FRED MSRs

> 
>> @@ -4316,6 +4374,12 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> #endif
>> case MSR_IA32_U_CET:
>> case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
>> + if (!guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {
>> + WARN_ON_ONCE(msr != MSR_IA32_FRED_SSP0);
> 
> This will be triggered if the guest only supports IBT and tries to write U_CET here.

You’re right, my stupid.