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

[Dave Jones <davej@redhat.com>]

On Fri, Jan 18, 2008 at 10:02:10PM +0100, Ingo Molnar wrote:
 > 
 > * Dave Jones <davej@redhat.com> 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.

	Dave

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