lkml.org 
[lkml]   [2014]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH 1/5] x86, mm, pat: Set WT to PA4 slot of PAT MSR
    On Thu, Sep 4, 2014 at 5:29 PM, Toshi Kani <toshi.kani@hp.com> wrote:
    > On Thu, 2014-09-04 at 16:34 -0700, Andy Lutomirski wrote:
    >> 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. :)
    >
    > According to the spec, the upper four entries bug was fixed in Pentium 4
    > model 0x1. So, the remaining Intel 32-bit processors that may enable
    > the upper four entries are Pentium 4 model 0x1-4. Should we disable it
    > for all Pentium 4 models?

    Assuming that this is Pentium 4 erratum N46, then there may be another
    option: use slot 7 instead of slot 4 for WT. Then, even if somehow
    the blacklist screws up, the worst that happens is that a WT page gets
    interpreted as UC. I suppose this could cause aliasing issues, but
    can't cause problems for people who don't use the high entries in the
    first place.

    --Andy

    >
    > Thanks,
    > -Toshi
    >



    --
    Andy Lutomirski
    AMA Capital Management, LLC


    \
     
     \ /
      Last update: 2014-09-05 03:21    [W:2.271 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site