linux-kernel - Re: [PATCH v5 13/19] KVM:VMX: Set up interception for CET MSRs

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Date:   Sun, 6 Aug 2023 17:22:53 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Chao Gao <chao.gao@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <peterz@...radead.org>,
        <john.allen@....com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
        <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v5 13/19] KVM:VMX: Set up interception for CET MSRs

On 8/4/2023 4:16 PM, Chao Gao wrote:
> On Thu, Aug 03, 2023 at 12:27:26AM -0400, Yang Weijiang wrote:
>> Pass through CET MSRs when the associated feature is enabled.
>> Shadow Stack feature requires all the CET MSRs to make it
>> architectural support in guest. IBT feature only depends on
>> MSR_IA32_U_CET and MSR_IA32_S_CET to enable both user and
>> supervisor IBT. Note, This MSR design introduced an architectual
>> limitation of SHSTK and IBT control for guest, i.e., when SHSTK
>> is exposed, IBT is also available to guest from architectual level
>> since IBT relies on subset of SHSTK relevant MSRs.
>>
>> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Reviewed-by: Chao Gao <chao.gao@...el.com>
>
> one nit below
Thanks!
> [...]
>> +
>> +	if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
>> +		incpt = !guest_can_use(vcpu, X86_FEATURE_IBT);
> can you use guest_can_use() or guest_cpuid_has() consistently?
Hmm, the inspiration actually came from Sean:
Re: [RFC PATCH v2 3/6] KVM: x86: SVM: Pass through shadow stack MSRs - Sean Christopherson (kernel.org) <https://lore.kernel.org/all/ZMk14YiPw9l7ZTXP@google.com/>
it would make the code more reasonable on non-CET platforms.
>> +
>> +		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET,
>> +					  MSR_TYPE_RW, incpt);
>> +		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET,
>> +					  MSR_TYPE_RW, incpt);
>> +	}
>> +}
>> +
>> static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>> {
>> 	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> @@ -7814,6 +7853,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>>
>> 	/* Refresh #PF interception to account for MAXPHYADDR changes. */
>> 	vmx_update_exception_bitmap(vcpu);
>> +
>> +	vmx_update_intercept_for_cet_msr(vcpu);
>> }
>>
>> static u64 vmx_get_perf_capabilities(void)
>> -- 
>> 2.27.0
>>