linux-kernel - Re: [patch V3 06/66] x86/fpu: Make xfeatures_mask_all __ro_after

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Date:   Sun, 20 Jun 2021 10:44:40 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch V3 06/66] x86/fpu: Make xfeatures_mask_all __ro_after_init

On Fri, Jun 18, 2021 at 04:18:29PM +0200, Thomas Gleixner wrote:
> Nothing has to modify this after init.
> 
> But of course there is code which unconditionaly masks xfeatures_mask_all

WARNING: 'unconditionaly' may be misspelled - perhaps 'unconditionally'?
#71: 
But of course there is code which unconditionaly masks xfeatures_mask_all
                                  ^^^^^^^^^^^^^^
> @@ -896,8 +888,18 @@ void __init fpu__init_system_xstate(void
>  	setup_init_fpu_buf();
>  	setup_xstate_comp_offsets();
>  	setup_supervisor_only_offsets();
> -	print_xstate_offset_size();
>  
> +	/*
> +	 * Paranoia check whether something in the setup modified the
> +	 * xfeatures mask.
> +	 */
> +	if (xfeatures != xfeatures_mask_all) {
> +		pr_err("x86/fpu: xfeatures modified during init %016llx %016llx, disabling XSAVE\n",

Let's make that:

		pr_err("x86/fpu: xfeatures modified from 0x%016llx to 0x%016llx during init, disabling XSAVE\n",

so that it is clear which is which.

With those:

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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