linux-kernel - Re: [PATCH 1/6] x86/fpu/xstate: Fix small issues before adding supervisor xstates

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Date:   Wed, 9 Oct 2019 17:58:47 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/6] x86/fpu/xstate: Fix small issues before adding
 supervisor xstates

On Wed, Sep 25, 2019 at 08:10:17AM -0700, Yu-cheng Yu wrote:
> In response to earlier comments, fix small issues before introducing XSAVES
> supervisor states:
> - Add spaces around '*'.
> - Fix comments of xfeature_is_supervisor().
> - Replace ((u64)1 << 63) with XCOMP_BV_COMPACTED_FORMAT.
> 
> No functional changes from this patch.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/fpu/xstate.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index e5cb67d67c03..b793fc2156b9 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -60,7 +60,7 @@ u64 xfeatures_mask __read_mostly;
>  
>  static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
>  static unsigned int xstate_sizes[XFEATURE_MAX]   = { [ 0 ... XFEATURE_MAX - 1] = -1};
> -static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
> +static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask) * 8];
>  
>  /*
>   * The XSAVE area of kernel can be in standard or compacted format;
> @@ -110,12 +110,8 @@ EXPORT_SYMBOL_GPL(cpu_has_xfeatures);
>  static int xfeature_is_supervisor(int xfeature_nr)
>  {
>  	/*
> -	 * We currently do not support supervisor states, but if
> -	 * we did, we could find out like this.
> -	 *
> -	 * SDM says: If state component 'i' is a user state component,
> -	 * ECX[0] return 0; if state component i is a supervisor
> -	 * state component, ECX[0] returns 1.
> +	 * Extended State Enumeration Sub-leaves (EAX = 0DH, ECX = n, n > 1)
> +	 * returns ECX[0] set to (1) for a supervisor state.

"... and cleared (0) for a user state."

I believe it is is clearer this way.

>  	 */
>  	u32 eax, ebx, ecx, edx;
>  

Since you're touching this function: make it return bool as it is used
in boolean context only and have it return simply:

	return ecx & 1;

Thx.

-- 
Regards/Gruss,
    Boris.

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