linux-kernel - Re: [PATCH v15 16/41] KVM: VMX: Set up interception for CET MSRs

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Message-ID: <254ecddb-1bc3-4126-8256-9ef7044865de@intel.com>
Date: Tue, 16 Sep 2025 15:40:33 +0800
From: Xiaoyao Li <xiaoyao.li@...el.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>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v15 16/41] KVM: VMX: Set up interception for CET MSRs

On 9/13/2025 7:22 AM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@...el.com>
> 
> Enable/disable CET MSRs interception per associated feature configuration.
> 
> Pass through CET MSRs that are managed by XSAVE, as they cannot be
> intercepted without also intercepting XSAVE. However, intercepting XSAVE
> would likely cause unacceptable performance overhead.
> MSR_IA32_INT_SSP_TAB is not managed by XSAVE, so it is intercepted.
> 
> Note, this MSR design introduced an architectural limitation of SHSTK and
> IBT control for guest, i.e., when SHSTK is exposed, IBT is also available
> to guest from architectural perspective since IBT relies on subset of SHSTK
> relevant MSRs.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> 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: Xiaoyao Li <xiaoyao.li@...el.com>