linux-kernel - Re: [patch V163 38/51] x86/mm/64: Make a full PGD-entry size hole in the memory map

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Message-ID: <20171218132727.43umqlu4hirgwhlf@hirez.programming.kicks-ass.net>
Date:   Mon, 18 Dec 2017 14:27:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
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>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bpetkov@...e.de>,
        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,
        Kees Cook <keescook@...omium.org>,
        Borislav Petkov <bp@...en8.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [patch V163 38/51] x86/mm/64: Make a full PGD-entry size hole in
 the memory map

On Mon, Dec 18, 2017 at 12:42:53PM +0100, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@...nel.org>
> 
> Shrink 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.

The below patch only changes 5L things, what about 4L ?

> ---
>  Documentation/x86/x86_64/mm.txt         |    4 ++--
>  arch/x86/include/asm/pgtable_64_types.h |    4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> --- a/Documentation/x86/x86_64/mm.txt
> +++ b/Documentation/x86/x86_64/mm.txt
> @@ -28,8 +28,8 @@ ffffffffffe00000 - ffffffffffffffff (=2
>  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 (12800 TB)
>  ffd2000000000000 - ffd3ffffffffffff (=49 bits) hole
>  ffd4000000000000 - ffd5ffffffffffff (=49 bits) virtual memory map (512TB)
>  ... unused hole ...
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -78,8 +78,8 @@ typedef struct { pteval_t pte; } pte_t;
>  /* See Documentation/x86/x86_64/mm.txt for a description of the memory map. */
>  #define MAXMEM		_AC(__AC(1, UL) << MAX_PHYSMEM_BITS, UL)
>  #ifdef CONFIG_X86_5LEVEL
> -#define VMALLOC_SIZE_TB _AC(16384, UL)
> -#define __VMALLOC_BASE	_AC(0xff92000000000000, UL)
> +#define VMALLOC_SIZE_TB _AC(12800, UL)
> +#define __VMALLOC_BASE	_AC(0xffa0000000000000, UL)
>  #define __VMEMMAP_BASE	_AC(0xffd4000000000000, UL)
>  #else
>  #define VMALLOC_SIZE_TB	_AC(32, UL)
> 
>