linux-kernel - Re: [PATCH PTI v3 09/10] x86/mm/64: Make a full PGD-entry size hole in the memory map

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Date:   Wed, 13 Dec 2017 16:17:17 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH PTI v3 09/10] x86/mm/64: Make a full PGD-entry size hole
 in the memory map

On Tue, Dec 12, 2017 at 07:56:44AM -0800, Andy Lutomirski wrote:
> This patch shrinks vmalloc space from 16384TiB to 12800TiB to
> enlarge the hole starting at 0xff90000000000000 to be a full PGD
> entry.
> 
> A subsequent patch will use this hole for the pagetable isolation
> LDT alias.
> 
> Cc: "Kirill A. Shutemov" <kirill@...temov.name>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  Documentation/x86/x86_64/mm.txt         | 4 ++--
>  arch/x86/include/asm/pgtable_64_types.h | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/x86/x86_64/mm.txt b/Documentation/x86/x86_64/mm.txt
> index 63a41671d25b..6a28aeaccd53 100644
> --- a/Documentation/x86/x86_64/mm.txt
> +++ b/Documentation/x86/x86_64/mm.txt
> @@ -28,8 +28,8 @@ Virtual memory map with 5 level page tables:
>  hole caused by [56:63] sign extension
>  ff00000000000000 - ff0fffffffffffff (=52 bits) guard hole, reserved for hypervisor
>  ff10000000000000 - ff8fffffffffffff (=55 bits) direct mapping of all phys. memory
> -ff90000000000000 - ff91ffffffffffff (=49 bits) hole
> -ff92000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space
> +ff90000000000000 - ff9fffffffffffff (=52 bits) hole
> +ffa0000000000000 - ffd1ffffffffffff (=54 bits) vmalloc/ioremap space

It's not 54 bits anymore.

-- 
 Kirill A. Shutemov