linux-kernel - Re: [PATCH v7 02/26] x86/fpu/xstate: Refine CET user xstate bit enabling

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Message-ID: <a45c2e25aaa1f195e7fccff6114374994ffbc099.camel@intel.com>
Date:   Tue, 28 Nov 2023 01:31:14 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>,
        "Yang, Weijiang" <weijiang.yang@...el.com>
CC:     "Gao, Chao" <chao.gao@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "john.allen@....com" <john.allen@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "mlevitsk@...hat.com" <mlevitsk@...hat.com>
Subject: Re: [PATCH v7 02/26] x86/fpu/xstate: Refine CET user xstate bit
 enabling

On Fri, 2023-11-24 at 10:40 +0100, Peter Zijlstra wrote:
> So booting a host with "ibt=off" will clear the FEATURE_IBT, this was
> fine before this patch-set, but possibly not with.
> 
> That kernel argument really only wants to tell the kernel not to use
> IBT
> itself, but not inhibit IBT from being used by guests.

Should we add a SW bit for it then? ibt=off sounds like it should be
turning off the whole feature though. It doesn't sound like kernel IBT
specifically.