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    SubjectRe: [PATCH 1/5] x86, mm, pat: Set WT to PA4 slot of PAT MSR
    On Thu, Sep 4, 2014 at 4:19 PM, Henrique de Moraes Holschuh
    <hmh@hmh.eng.br> wrote:
    > On Thu, 04 Sep 2014, H. Peter Anvin wrote:
    >> On 09/04/2014 01:11 PM, Henrique de Moraes Holschuh wrote:
    >> > I am worried of uncharted territory, here. I'd actually advocate for not
    >> > enabling the upper four PAT entries on IA-32 at all, unless Windows 9X / XP
    >> > is using them as well. Is this a real concern, or am I being overly
    >> > cautious?
    >>
    >> It is extremely unlikely that we'd have PAT issues in 32-bit mode and
    >> not in 64-bit mode on the same CPU.
    >
    > Sure, but is it really a good idea to enable this on the *old* non-64-bit
    > capable processors (note: I don't mean x86-64 processors operating in 32-bit
    > mode) ?
    >
    >> As far as I know, the current blacklist rule is very conservative due to
    >> lack of testing more than anything else.
    >
    > I was told that much in 2009 when I asked why cpuid 0x6d8 was blacklisted
    > from using PAT :-)

    At the very least, anyone who plugs an NV-DIMM into a 32-bit machine
    is nuts, and not just because I'd be somewhat amazed if it even
    physically fits into the slot. :)

    --Andy

    >
    > --
    > "One disk to rule them all, One disk to find them. One disk to bring
    > them all and in the darkness grind them. In the Land of Redmond
    > where the shadows lie." -- The Silicon Valley Tarot
    > Henrique Holschuh



    --
    Andy Lutomirski
    AMA Capital Management, LLC


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