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Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>
References: <20220130211838.8382-1-rick.p.edgecombe@intel.com>
 <20220130211838.8382-4-rick.p.edgecombe@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH 03/35] x86/cpufeatures: Add CET CPU feature flags for
 Control-flow Enforcement Technology (CET)
In-Reply-To: <20220130211838.8382-4-rick.p.edgecombe@intel.com>
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On 1/30/22 13:18, Rick Edgecombe wrote:
> --- a/arch/x86/kernel/cpu/cpuid-deps.c
> +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> @@ -78,6 +78,7 @@ static const struct cpuid_dep cpuid_deps[] = {
>  	{ X86_FEATURE_XFD,			X86_FEATURE_XSAVES    },
>  	{ X86_FEATURE_XFD,			X86_FEATURE_XGETBV1   },
>  	{ X86_FEATURE_AMX_TILE,			X86_FEATURE_XFD       },
> +	{ X86_FEATURE_SHSTK,			X86_FEATURE_XSAVES    },
>  	{}
>  };

Please add a chunk to the changelog that explains the dependency.  This
would suffice:

	To protect shadow stack state from malicious modification, the
	registers are only accessible in supervisor mode.  This
	implementation context-switches the registers with XSAVES.  Make
	X86_FEATURE_SHSTK depend on XSAVES.

The XSAVES dependency is touched on in the documentation, but it's a bit
buried in there.