linux-kernel - Re: [PATCH v14 11/22] KVM: VMX: Emulate read and write to CET MSRs

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Message-ID: <aMKQO8+XwWF5UOSR@intel.com>
Date: Thu, 11 Sep 2025 17:02:51 +0800
From: Chao Gao <chao.gao@...el.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <acme@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
	<john.allen@....com>, <mingo@...nel.org>, <mingo@...hat.com>,
	<minipli@...ecurity.net>, <mlevitsk@...hat.com>, <namhyung@...nel.org>,
	<pbonzini@...hat.com>, <prsampat@....com>, <rick.p.edgecombe@...el.com>,
	<seanjc@...gle.com>, <shuah@...nel.org>, <tglx@...utronix.de>,
	<weijiang.yang@...el.com>, <x86@...nel.org>, <xin@...or.com>
Subject: Re: [PATCH v14 11/22] KVM: VMX: Emulate read and write to CET MSRs

On Thu, Sep 11, 2025 at 04:05:23PM +0800, Xiaoyao Li wrote:
>On 9/9/2025 5:39 PM, Chao Gao wrote:
>> From: Yang Weijiang <weijiang.yang@...el.com>
>> 
>> Add emulation interface for CET MSR access. The emulation code is split
>> into common part and vendor specific part. The former does common checks
>> for MSRs, e.g., accessibility, data validity etc., then passes operation
>> to either XSAVE-managed MSRs via the helpers or CET VMCS fields.
>
>I planed to continue the review after Sean posts v15 as he promised.
>But I want to raise my question regarding it sooner so I just ask it on v14.
>
>Do we expect to put the accessibility and data validity check always in
>__kvm_{s,g}_msr(), when the handling cannot be put in kvm_{g,s}et_common()
>only? i.e., there will be 3 case:

For checks that are shared between VMX/SVM, I think yes and there is no other
sensible choice to me; other options just cause code duplication. For checks
that are not common, we have to put them into vendor code.

>
>- All the handling in kvm_{g,s}et_common(), when the MSR emulation is common
>to vmx and svm.
>
>- generic accessibility and data validity check in __kvm_{g,s}et_msr() and
>vendor specific handling in {vmx,svm}_{g,s}et_msr()
>
>- generic accessibility and data validity check in __kvm_{g,s}et_msr() ,
>vendor specific handling in {vmx,svm}_{g,s}et_msr() and other generic
>handling in kvm_{g,s}et_common()