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