linux-kernel - Re: [PATCH 04/19] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states

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Date:   Thu, 16 Jun 2022 17:12:08 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>,
        "Yang, Weijiang" <weijiang.yang@...el.com>
CC:     "keescook@...omium.org" <keescook@...omium.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/19] x86/fpu/xstate: Introduce CET MSR and XSAVES
 supervisor states

On Thu, 2022-06-16 at 12:27 +0200, Peter Zijlstra wrote:
> On Thu, Jun 16, 2022 at 04:46:28AM -0400, Yang Weijiang wrote:
> > diff --git a/arch/x86/include/asm/fpu/types.h
> > b/arch/x86/include/asm/fpu/types.h
> > index eb7cd1139d97..03aa98fb9c2b 100644
> > --- a/arch/x86/include/asm/fpu/types.h
> > +++ b/arch/x86/include/asm/fpu/types.h
> > @@ -115,8 +115,8 @@ enum xfeature {
> >        XFEATURE_PT_UNIMPLEMENTED_SO_FAR,
> >        XFEATURE_PKRU,
> >        XFEATURE_PASID,
> > -     XFEATURE_RSRVD_COMP_11,
> > -     XFEATURE_RSRVD_COMP_12,
> > +     XFEATURE_CET_USER,
> > +     XFEATURE_CET_KERNEL_UNIMPLEMENTED_SO_FAR,
> >        XFEATURE_RSRVD_COMP_13,
> >        XFEATURE_RSRVD_COMP_14,
> >        XFEATURE_LBR,
> > @@ -138,6 +138,8 @@ enum xfeature {
> >   #define XFEATURE_MASK_PT             (1 <<
> > XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
> >   #define XFEATURE_MASK_PKRU           (1 << XFEATURE_PKRU)
> >   #define XFEATURE_MASK_PASID          (1 << XFEATURE_PASID)
> > +#define XFEATURE_MASK_CET_USER               (1 <<
> > XFEATURE_CET_USER)
> > +#define XFEATURE_MASK_CET_KERNEL     (1 <<
> > XFEATURE_CET_KERNEL_UNIMPLEMENTED_SO_FAR)
> >   #define XFEATURE_MASK_LBR            (1 << XFEATURE_LBR)
> >   #define XFEATURE_MASK_XTILE_CFG              (1 <<
> > XFEATURE_XTILE_CFG)
> >   #define XFEATURE_MASK_XTILE_DATA     (1 << XFEATURE_XTILE_DATA)
> 
> I'm not sure about that UNIMPLEMENTED_SO_FAR thing, that is, I'm
> thinking we *never* want XSAVE managed S_CET.

Hmm, yes. I mostly was just keeping the pattern with
XFEATURE_PT_UNIMPLEMENTED_SO_FAR.

How about XFEATURE_CET_KERNEL_UNUSED?