Re: 36 bit MTRRs, Re: test10-pre1 problems on 4-way SuperServer8050

From: Boszormenyi Zoltan (
Date: Thu Oct 12 2000 - 04:39:08 EST

On Thu, 12 Oct 2000, Tigran Aivazian wrote:
> suggestions?

I looked at what you sent (e820 map and lspci output) and came up with

Cover 6 GB with write-back, the VGA memory with write-combining, and
all the other PCI areas as uncached.

echo "base=0 size=0x100000000 type=write-back" >/proc/mtrr
echo "base=0x100000000 size=0x80000000 type=write-back" >/proc/mtrr
echo "base=0xfe000000 size=0x800000 type=write-combining" >/proc/mtrr
echo "base=0xfde00000 size=0x100000 type=uncached" >/proc/mtrr
echo "base=0xfe800000 size=0x100000 type=uncached" >/proc/mtrr
echo "base=0xfe9ed000 size=0x1000 type=uncached" >/proc/mtrr
echo "base=0xfe9ee000 size=0x2000 type=uncached" >/proc/mtrr
echo "base=0xfeafe000 size=0x2000 type=uncached" >/proc/mtrr

Do not be bothered about the 640K-1MB area because this is
handled by the so called fixed MTRRs, they are invisible in

It is possible that the above causes an (almost) immediate lockup because
of this line:

 BIOS-e820: 0000000000080000 @ 00000000fff80000 (reserved)

These are most likely memory mapped registers of the mainboard chipset
and I successfully locked up my home machine (ABit BP6, a BX mainboard)
with covering all 4GB with either write-back or write-combining.
(I do not remember which type it was.) Uncaching this area helped.

So experiment with leaving out the VGA memory from the above
lines and maybe the two 1MB areas (ethernet controllers' onboard
memory?) and uncaching this area:

echo "base=0xfff80000 size=0x80000 type=uncached" >/proc/mtrr

Zoltan Boszormenyi

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