linux-kernel - Re: [PATCH 4/3] x86/mm/doc: Enhance the x86-64 virtual memory layout descriptions

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Date:   Sat, 6 Oct 2018 14:33:22 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Baoquan He <bhe@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-doc@...r.kernel.org, tglx@...utronix.de, thgarnie@...gle.com,
        corbet@....net, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/3] x86/mm/doc: Enhance the x86-64 virtual memory layout
 descriptions


* Ingo Molnar <mingo@...nel.org> wrote:

> +========================================================
> +| Complete virtual memory map with 4-level page tables |
> +========================================================

> +--------------------------------------------------------------------------------
> +start addr       | offset     | end addr         |  size   | VM area description
> +-----------------|------------|------------------|---------|--------------------

> +
> +# Identical layout to the 56-bit one from here on:
> +
> +ffffff8000000000 | -512    GB | fffffffeefffffff | ~507 GB | ... unused hole
> +ffffffef00000000 |  -68    GB | fffffffeffffffff |   64 GB | EFI region mapping space

> +========================================================
> +| Complete virtual memory map with 5-level page tables |
> +========================================================

> +ffffff8000000000 |   -0.5  TB | ffffffeeffffffff |  444 GB | ... unused hole
> +
> +# Identical layout to the 47-bit one from here on:
> +
> +ffffffef00000000 |  -68    GB | fffffffeffffffff |   64 GB | EFI region mapping space

So patch #2 appears to have introduced an error/typo in the 47-bit table. Note the weird size 
and discontinuity of the 'unused hole' in the 47-bit table, and compare it with 56-bit table:

  fffffffeefffffff
  ffffffeeffffffff

(Note how the incorrect end address was cargo-cult-copied into the 'size' field of ~507 GB...)

The correct number is the 56-bit one, and both tables should show the following identical 
layout:

  ffffff8000000000 | -512    GB | fffffffeefffffff |  444 GB | ... unused hole
  ffffffef00000000 |  -68    GB | fffffffeffffffff |   64 GB | EFI region mapping space

Agreed?

Thanks,

	Ingo