linux-kernel - Re: [patch 39/60] x86/mm/kpti: Share cpu_entry

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Date:   Wed, 6 Dec 2017 22:18:00 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com,
        hughd@...gle.com, Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>, daniel.gruss@...k.tugraz.at
Subject: Re: [patch 39/60] x86/mm/kpti: Share cpu_entry_area PMDs

On Mon, Dec 04, 2017 at 03:07:45PM +0100, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@...nel.org>
> 
> Share the FIX_USR_SHARED PMDs so the user space and kernel space page
> tables have the same PMD page.
> 
> [ tglx: Made it use the FIX_USR_SHARED range so later additions
>   	are covered automatically ]
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/mm/kpti.c |   18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> --- a/arch/x86/mm/kpti.c
> +++ b/arch/x86/mm/kpti.c
> @@ -167,6 +167,23 @@ kpti_clone_pmds(unsigned long start, uns
>  }
>  
>  /*
> + * Clone the populated PMDs of the user shared fixmaps into the user space
> + * visible page table.
> + */
> +static void __init kpti_clone_user_shared(void)
> +{
> +	unsigned long bot, top;
> +
> +	bot = __fix_to_virt(FIX_USR_SHARED_BOTTOM);
> +	top = __fix_to_virt(FIX_USR_SHARED_TOP) + PAGE_SIZE;
> +
> +	/* Top of the user shared block must be PMD-aligned. */
> +	WARN_ON(top & ~PMD_MASK);

Or

	WARN_ON(top & (PMD_SIZE - 1));


Otherwise:

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

-- 
Regards/Gruss,
    Boris.

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