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

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Date:   Wed, 6 Dec 2017 21:56:05 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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


* Borislav Petkov <bp@...e.de> wrote:

> 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"

Fixed. I also did a s/pgd/PGD

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

Thanks!

	Ingo