linux-kernel - Re: [PATCH v5 3/7] x86/fpu/xstate: Differentiate default features for host and guest FPUs

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Message-ID: <853c6f7c-b4ea-4c25-8816-856bb56895bc@zytor.com>
Date: Sun, 27 Apr 2025 23:31:05 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>,
        Rick P Edgecombe <rick.p.edgecombe@...el.com>
Cc: Chao Gao <chao.gao@...el.com>,
        "kvm@...r.kernel.org"
 <kvm@...r.kernel.org>,
        "ebiggers@...gle.com" <ebiggers@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Stanislav Spassov <stanspas@...zon.de>,
        "levymitchell0@...il.com" <levymitchell0@...il.com>,
        "samuel.holland@...ive.com" <samuel.holland@...ive.com>,
        Xin3 Li <xin3.li@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "mingo@...hat.com"
 <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "john.allen@....com" <john.allen@....com>,
        "mlevitsk@...hat.com" <mlevitsk@...hat.com>,
        Chang Seok Bae <chang.seok.bae@...el.com>,
        "vigbalas@....com" <vigbalas@....com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com"
 <hpa@...or.com>, "bp@...en8.de" <bp@...en8.de>,
        "aruna.ramakrishna@...cle.com" <aruna.ramakrishna@...cle.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v5 3/7] x86/fpu/xstate: Differentiate default features for
 host and guest FPUs

On 4/25/2025 4:48 PM, Sean Christopherson wrote:
> CET_S probably shouldn't be in XSAVE ABI, because that would technically leak
> kernel state to userspace for the non-KVM use case.  I assume the kernel has
> bigger problems if CET_S is somehow tied to a userspace task.

+1000