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Date:   Mon, 12 Oct 2020 22:58:08 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
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        Jonathan Corbet <corbet@lwn.net>,
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        Mike Kravetz <mike.kravetz@oracle.com>,
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        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
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        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>
Subject: Re: [PATCH v14 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES
 supervisor states
Message-ID: <20201012195808.GD14048@grain>
References: <20201012153850.26996-1-yu-cheng.yu@intel.com>
 <20201012153850.26996-4-yu-cheng.yu@intel.com>
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On Mon, Oct 12, 2020 at 08:38:27AM -0700, Yu-cheng Yu wrote:
...
>  /*
>   * x86-64 Task Priority Register, CR8
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 038e19c0019e..705fd9b94e31 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -38,6 +38,9 @@ static const char *xfeature_names[] =
>  	"Processor Trace (unused)"	,
>  	"Protection Keys User registers",
>  	"unknown xstate feature"	,
> +	"Control-flow User registers"	,
> +	"Control-flow Kernel registers"	,
> +	"unknown xstate feature"	,
>  };
>  
>  static short xsave_cpuid_features[] __initdata = {
> @@ -51,6 +54,9 @@ static short xsave_cpuid_features[] __initdata = {
>  	X86_FEATURE_AVX512F,
>  	X86_FEATURE_INTEL_PT,
>  	X86_FEATURE_PKU,
> +	-1,		   /* Unused */
> +	X86_FEATURE_SHSTK, /* XFEATURE_CET_USER */
> +	X86_FEATURE_SHSTK, /* XFEATURE_CET_KERNEL */
>  };

Why do you need "-1" here in the array? The only 1:1 mapping is between
the names itselves and values, not indices of arrays so i don't understand
why we need this unused value. Sorry if it is a dumb questions and
been discussed already.