lkml.org 
[lkml]   [2007]   [Sep]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: MTRR initialization
Date
"Yinghai Lu" <yhlu.kernel@gmail.com> writes:

> On 9/16/07, Howard Chu <hyc@symas.com> wrote:
>> Yinghai Lu wrote:
>> > On 9/14/07, Howard Chu <hyc@symas.com> wrote:
>> >> Hi, was wondering if anyone else has been tripped up by this... I've got
> 4GB of
>> >> RAM in my Asus A8V Deluxe and memory hole mapping enabled in the BIOS. By
>> >> default, my system boots up with these MTRR settings:
>> >>
>> >> reg00: base=0x00000000 ( 0MB), size=4096MB: write-back, count=1
>> >> reg01: base=0x100000000 (4096MB), size=1024MB: write-back, count=1
>> >> reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1
>> >> reg03: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1
>
> if rev F before cpu aka Rev E is installed, and 8G RAM installed, it will be
>> >> reg00: base=0x00000000 ( 0MB), size=8192MB: write-back, count=1
>> >> reg01: base=0x100000000 (8192MB), size=1024MB: write-back, count=1
>> >> reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1
>> >> reg03: base=0xc0000000 (3072MB), size= 256MB: write-combining, count=1
> and you will have problem...
>
> So good way is get the ram top, and hole size...and reset the whole
> set ot var mtrr.
>
> you could refer the code in LinuxBIOS about setting that...
> http://www.openbios.org/viewvc/trunk/LinuxBIOSv2/src/cpu/x86/mtrr/mtrr.c?revision=2616&view=markup
> esp the part about CONFIG_VAR_MTRR_HOLE...
>
> but Andi and Eric said resetting mtrr is not good... when someone from
> intel try to trim the MTRR for intel CPU.

There are a couple issues with changing the MTRR configuration.
- You may not have perfect information on the cpu, the AMD revF is a good
example.
- Code in SMM mode may actually depend on the current mtrr configuration.
- The BIOS's need to fixed to setup MTRRs properly.

So the sanest approach appears to be.
- In linux only use ram that is mapped by a write-back mtrr.
This preserves performance and is always safe.
- If you need write-combining set it up in the page tables with PAT.

There is some difficulty there but software can always do those things
safely.

Eric
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-09-16 20:43    [W:0.123 / U:0.632 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site