linux-kernel - Re: [PATCH] x86: add phys addr validity check for /dev/mem mmap

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Message-ID: <51662492.1030100@zytor.com>
Date:	Wed, 10 Apr 2013 19:48:50 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Simon Jeons <simon.jeons@...il.com>
CC:	Frantisek Hrbata <fhrbata@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	oleg@...hat.com, kamaleshb@...ibm.com
Subject: Re: [PATCH] x86: add phys addr validity check for /dev/mem mmap

On 04/10/2013 07:40 PM, Simon Jeons wrote:
> Hi H.Peter,
> On 04/04/2013 09:13 AM, H. Peter Anvin wrote:
>> On 04/03/2013 06:11 PM, Simon Jeons wrote:
>>> Why we consider boot_cpu_data.x86_phys_bits instead of e820 map here?
>>>
>> Because x86_phys_bits is what controls how much address space the
>> processor has.  e820 tells us how much *RAM* the machine has, or
>> specifically, how much RAM the machine had on boot.
> 
> I have 8GB memory in my machine, but when I accumulated every e820
> ranges which dump in dmesg, there are 25MB memory less then 8GB(1024*8)
> memory, why 25MB miss?
> 

For whatever reason your BIOS is stealing some memory, possibly for video.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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