linux-kernel - Re: [PATCH 03/16] x86/gdt: Put per-cpu GDT remaps in ascending order

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Message-ID: <20171121171643.jtwbfuvxwi6wecj3@pd.tnic>
Date:   Tue, 21 Nov 2017 18:16:43 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 03/16] x86/gdt: Put per-cpu GDT remaps in ascending order

On Mon, Nov 20, 2017 at 09:07:34AM -0800, Andy Lutomirski wrote:
> We currently have CPU 0's GDT at the top of the GDT range and
> higher-numbered CPUs at lower addreses.  This happens because the

addresses

> fixmap is upside down (index 0 is the top of the fixmap).
> 
> Flip it so that GDTs are in ascending order by virtual address.
> This will simplify a future patch that will generalize the GDT
> remap to contain multiple pages.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/include/asm/desc.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
> index 4011cb03ef08..95cd95eb7285 100644
> --- a/arch/x86/include/asm/desc.h
> +++ b/arch/x86/include/asm/desc.h
> @@ -63,7 +63,7 @@ static inline struct desc_struct *get_current_gdt_rw(void)
>  /* Get the fixmap index for a specific processor */
>  static inline unsigned int get_cpu_gdt_ro_index(int cpu)
>  {
> -	return FIX_GDT_REMAP_BEGIN + cpu;
> +	return FIX_GDT_REMAP_END - cpu;
>  }
>  
>  /* Provide the fixmap address of the remapped GDT */
> -- 

Other than the typo above:

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

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--