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Date: Fri, 18 Jan 2008 22:28:49 -0500 From: Dave Jones <davej@...hat.com> To: Ingo Molnar <mingo@...e.hu> Cc: Yinghai Lu <Yinghai.Lu@....COM>, venkatesh.pallipadi@...el.com, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] X86: fix typo PAT to X86_PAT On Fri, Jan 18, 2008 at 10:02:10PM +0100, Ingo Molnar wrote: > > * Dave Jones <davej@...hat.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 -- http://www.codemonkey.org.uk -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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