linux-kernel - Re: x86_64: Question about fixmaps

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Message-ID: <552DB0BE.5020305@amacapital.net>
Date:	Tue, 14 Apr 2015 17:28:46 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Alexander Kuleshov <alex0xax@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: x86_64: Question about fixmaps

On 04/14/2015 06:16 AM, Alexander Kuleshov wrote:
> Hello All,
>
> I'm reading x86_64 source code and trying to understand where are
> fixmaps space in the virtual memory space. If I understand correctly
> (but i'm really not sure about it), fixmap space is after vsyscall
> space. As Documentation/x86/x86_64/mm.txt says vsyscall virtual space
> is:
>
> ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
>
> With 'earlyprintk' i got FIXADDR_START and FIXADDR_TOP and they are:
>
> FIXADDR_START -  0xffffffffff779000L
> FIXADDR_TOP     -  0xffffffffff7ff000L
>
> with these addressess FIXADDR_START/FIXADDR_TOP overlap vsyscalls
> area. Is it correct case that fixmaps are in vsyscal virtual memory
> space or I'm wrong somewhere?

It's the other way around.  vsyscalls are in the fixmap.  I should fix 
the docs.

--Andy
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