linux-kernel - Re: [PATCH v17 04/26] x86/cpufeatures: Introduce X86_FEATURE

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Date:   Mon, 11 Jan 2021 18:56:43 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v17 04/26] x86/cpufeatures: Introduce X86_FEATURE_CET and
 setup functions

On Tue, Dec 29, 2020 at 01:30:31PM -0800, Yu-cheng Yu wrote:
> @@ -895,6 +903,12 @@ static void init_speculation_control(struct cpuinfo_x86 *c)
>  	}
>  }
>  
> +static void init_cet_features(struct cpuinfo_x86 *c)
> +{
> +	if (cpu_has(c, X86_FEATURE_SHSTK) || cpu_has(c, X86_FEATURE_IBT))
> +		set_cpu_cap(c, X86_FEATURE_CET);
> +}

No need for that function - just add this two-liner to bsp_init_intel()
and not in get_cpu_cap().

> +static void adjust_combined_cpu_features(void)
> +{
> +#ifdef CONFIG_X86_CET_USER
> +	if (test_bit(X86_FEATURE_SHSTK, (unsigned long *)cpu_caps_cleared) &&
> +	    test_bit(X86_FEATURE_IBT, (unsigned long *)cpu_caps_cleared))
> +		setup_clear_cpu_cap(X86_FEATURE_CET);
> +#endif

There's no need for this function...

> +}
> +
>  /*
>   * We parse cpu parameters early because fpu__init_system() is executed
>   * before parse_early_param().
> @@ -1252,9 +1276,19 @@ static void __init cpu_parse_early_param(void)
>  	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
>  		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
>  
> +	/*
> +	 * CET states are XSAVES states and options must be parsed early.
> +	 */
> +#ifdef CONFIG_X86_CET_USER
> +	if (cmdline_find_option_bool(boot_command_line, "no_user_shstk"))
> +		setup_clear_cpu_cap(X86_FEATURE_SHSTK);

... when you can do

	setup_clear_cpu_cap(X86_FEATURE_CET);

here and...

> +	if (cmdline_find_option_bool(boot_command_line, "no_user_ibt"))
> +		setup_clear_cpu_cap(X86_FEATURE_IBT);

... here.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette