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    SubjectRe: [Bug 11388] New: 2.6.27-rc3 warns about MTRR range; only 3 of 16gb of memory is usable

    * Yinghai Lu <yhlu.kernel@gmail.com> wrote:

    > or please try attached workaround patch. hope it works.
    >
    > Ingo,
    > if it works, we need to push it for 2.6.27

    i've tidied up your patch (see the commit below) and have queued it up
    in x86/urgent. It seems fairly safe and i guess we can push it to
    v2.6.27 if Joshua reports test success. Joshua, could you give it a go
    please?

    Ingo

    -------------->
    From 38cc1c3df77c1bb739a4766788eb9fa49f16ffdf Mon Sep 17 00:00:00 2001
    From: Yinghai Lu <yhlu.kernel@gmail.com>
    Date: Thu, 21 Aug 2008 20:24:24 -0700
    Subject: [PATCH] x86: work around MTRR mask setting

    Joshua Hoblitt reported that only 3 GB of his 16 GB of RAM is
    usable. Booting with mtrr_show showed us the BIOS-initialized
    MTRR settings - which are all wrong.

    So the root cause is that the BIOS has not set the mask correctly:

    > [ 0.429971] MSR00000200: 00000000d0000000
    > [ 0.433305] MSR00000201: 0000000ff0000800
    > should be ==> [ 0.433305] MSR00000201: 0000003ff0000800
    >
    > [ 0.436638] MSR00000202: 00000000e0000000
    > [ 0.439971] MSR00000203: 0000000fe0000800
    > should be ==> [ 0.439971] MSR00000203: 0000003fe0000800
    >
    > [ 0.443304] MSR00000204: 0000000000000006
    > [ 0.446637] MSR00000205: 0000000c00000800
    > should be ==> [ 0.446637] MSR00000205: 0000003c00000800
    >
    > [ 0.449970] MSR00000206: 0000000400000006
    > [ 0.453303] MSR00000207: 0000000fe0000800
    > should be ==> [ 0.453303] MSR00000207: 0000003fe0000800
    >
    > [ 0.456636] MSR00000208: 0000000420000006
    > [ 0.459970] MSR00000209: 0000000ff0000800
    > should be ==> [ 0.459970] MSR00000209: 0000003ff0000800

    So detect this borkage and add the prefix 111.

    Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
    Cc: <stable@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86/kernel/cpu/mtrr/generic.c | 15 +++++++++++++--
    1 files changed, 13 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
    index 509bd3d..43102e0 100644
    --- a/arch/x86/kernel/cpu/mtrr/generic.c
    +++ b/arch/x86/kernel/cpu/mtrr/generic.c
    @@ -379,6 +379,7 @@ static void generic_get_mtrr(unsigned int reg, unsigned long *base,
    unsigned long *size, mtrr_type *type)
    {
    unsigned int mask_lo, mask_hi, base_lo, base_hi;
    + unsigned int tmp, hi;

    rdmsr(MTRRphysMask_MSR(reg), mask_lo, mask_hi);
    if ((mask_lo & 0x800) == 0) {
    @@ -392,8 +393,18 @@ static void generic_get_mtrr(unsigned int reg, unsigned long *base,
    rdmsr(MTRRphysBase_MSR(reg), base_lo, base_hi);

    /* Work out the shifted address mask. */
    - mask_lo = size_or_mask | mask_hi << (32 - PAGE_SHIFT)
    - | mask_lo >> PAGE_SHIFT;
    + tmp = mask_hi << (32 - PAGE_SHIFT) | mask_lo >> PAGE_SHIFT;
    + mask_lo = size_or_mask | tmp;
    + /* Expand tmp with high bits to all 1s*/
    + hi = fls(tmp);
    + if (hi > 0) {
    + tmp |= ~((1<<(hi - 1)) - 1);
    +
    + if (tmp != mask_lo) {
    + WARN_ON("mtrr: your BIOS has set up an incorrect mask, fixing it up.\n");
    + mask_lo = tmp;
    + }
    + }

    /* This works correctly if size is a power of two, i.e. a
    contiguous range. */

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