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    SubjectRe: [git pull] x86 PAT changes

    * Gabriel C <nix.or.die@googlemail.com> wrote:

    > Hi Ingo,
    >
    > When using an 64bit ( didn't got time to test 32bit now ) kernel[1]
    > with PAT enabled , kvm-intel does not work anymore.
    >
    > When modprobing kvm-intel , kvm is saying VT extension is disable by
    > BIOS which isn't true. When disabling PAT again ( no changes to BIOS )
    > kvm-intel works again here.
    >
    > Is that an known problem ?

    no, that side-effect was not known. Cc:-ed more folks.

    > If you need more infos just let me know.
    >
    > Gabriel
    >
    > [1] 2.6.25-05096-gb1721d0-dirty
    > with following patches :
    > http://lkml.org/lkml/2008/4/26/37
    > http://lkml.org/lkml/2008/4/26/24
    > http://lkml.org/lkml/2008/4/25/107

    thanks - that should be enough for now. We'll try to reproduce these
    problems.

    A blind guess: maybe it's the CONFIG_NONPROMISC_DEVMEM somehow breaks
    Qemu. With the patch below you'd be able to disable NONPROMISC_DEVMEM
    without disabling PAT.

    Ingo

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 4d350b5..4aa4180 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -1049,9 +1049,9 @@ config MTRR
    See <file:Documentation/mtrr.txt> for more information.

    config X86_PAT
    - def_bool y
    + bool
    prompt "x86 PAT support"
    - depends on MTRR && NONPROMISC_DEVMEM
    + depends on MTRR
    help
    Use PAT attributes to setup page level cache control.


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