Re: [PATCH] X86: fix typo PAT to X86_PAT

From: Yinghai Lu
Date: Sat Jan 19 2008 - 02:52:18 EST


On Friday 18 January 2008 07:28:49 pm Dave Jones wrote:
> On Fri, Jan 18, 2008 at 10:02:10PM +0100, Ingo Molnar wrote:
> >
> > * Dave Jones <davej@xxxxxxxxxx> wrote:
> >
> > > > you mean modifies MTRRs? Which code is that? (besides the
> > > > /proc/mtrr userspace API)
> > >
> > > This exclusion is going to be a real pain in the ass for distro
> > > kernels. It's impossible for example to build a kernel that will now
> > > support the MTRR-alike registers on the AMD K6/early Cyrix etc and
> > > also support PAT.
> > >
> > > Additionally, given people tend to update their kernels a lot more
> > > often than they update to a whole new version of X, it means until
> > > userspace has caught up, we can't ship a kernel with PAT supported, or
> > > else X gets a lot slower due to the missing mtrr support.
> >
> > there's no exclusion enforced right now, and if a CPU is PAT-incapable
> > (or if the kernel is booted nopat) then the MTRR bits should be usable.
> > But if we boot with PAT enabled, and Xorg gets /proc/mtrr wrong, we'll
> > see nasty crashes. If it gets them right, it should all still work just
> > fine. Is this ok? Then, in a year or two, distros can disable write
> > support to /proc/mtrr. Hm?
>
> A crazy idea just occured to me.. We could make /proc/mtrr an interface
> to set PAT on a range of memory. This would make it transparently work
> without any changes in X or anything else that sets them in userspace.

goog idea...

we need to make X86_PAT depend on MTRR in arch/x86/Kconfig

YH
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