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

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Message-ID: <20181006144153.GE5140@MiWiFi-R3L-srv>
Date:   Sat, 6 Oct 2018 22:41:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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

On 10/06/18 at 02:33pm, Ingo Molnar wrote:
> 
> * 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?

Yes, you are right. I wondered why the size is a weird unaligned value.
Sorry about that.

Thanks
Baoquan