linux-kernel - Re: [patch 33/60] x86/mm/kpti: Allocate a separate user PGD

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Message-ID: <20171205183321.paaz6exxpaagr7vk@pd.tnic>
Date:   Tue, 5 Dec 2017 19:33:21 +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,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [patch 33/60] x86/mm/kpti: Allocate a separate user PGD

On Mon, Dec 04, 2017 at 03:07:39PM +0100, Thomas Gleixner wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Kernel page table isolation requires to have two PGDs. One for the kernel,
> which contains the full kernel mapping plus the user space mapping and one
> for user space which contains the user space mappings and the minimal set
> of kernel mappings which are required by the architecture to be able to
> transition from and to user space.
> 
> Add the necessary preliminaries.
> 
> [ tglx: Split out from the big kaiser dump ]
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>  arch/x86/kernel/head_64.S |   30 +++++++++++++++++++++++++++---
>  arch/x86/mm/pgtable.c     |   16 ++++++++++++++--
>  2 files changed, 41 insertions(+), 5 deletions(-)

...

> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -355,14 +355,26 @@ static inline void _pgd_free(pgd_t *pgd)
>  		kmem_cache_free(pgd_cache, pgd);
>  }
>  #else
> +
> +#ifdef CONFIG_KERNEL_PAGE_TABLE_ISOLATION
> +/*
> + * Instead of one pgd, we aquire two pgds.  Being order-1, it is

"acquire"

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)
--