Re: [PATCH] Use global TLB flushes in MTRR code

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To: Andi Kleen <andi@...>
Cc: <davej@...>, <tglx@...>, <linux-kernel@...>, H. Peter Anvin <hpa@...>
Date: Saturday, February 9, 2008 - 7:47 am

* Andi Kleen <andi@firstfloor.org> wrote:


You are still dead wrong. You refuse to realize the _obvious_ and 
_fundamental_ thing that the PGE bit does: it enables global TLBs while 
we change MTRRs!

That would be a completely new and totally untested modus operandi for a 
large array of x86 CPUs. You should read the Intel manual about the 
recommended way to change MTRRs (Vol. 3A 10-41) - it describes disabling 
the PGE during MTRR changes if it's enabled. The primary purpose of that 
is of course to flush the TLB entries - but still it's documented that 
way and the current code does it that way. It would be rather stupid for 
us to do otherwise: we simply cannot guarantee that x86 CPUs that 
implement MTRRs and PGE have no undocumented or _unknown_ erratas in 
this area. It _might_ be fine, while what you say is that it _is_ fine - 
which we simply cannot know. (And yes, there are documented CPU erratas 
related to global TLBs and MTRR's, so this area is far from being an 
unwritten page.)

So i refuse to apply such a pointless and risky "cleanup" patch from you 
to arch/x86 [which increases code size as well], _especially_ given how 
many times i've explained this very issue to you already and especially 
because you continue to mislead about the true effects of the patch.

	Ingo
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Messages in current thread:
[PATCH] Use global TLB flushes in MTRR code, Andi Kleen, (Thu Feb 7, 3:02 pm)
Re: [PATCH] Use global TLB flushes in MTRR code, Ingo Molnar, (Thu Feb 7, 3:13 pm)
Re: [PATCH] Use global TLB flushes in MTRR code, Andi Kleen, (Thu Feb 7, 4:03 pm)
Re: [PATCH] Use global TLB flushes in MTRR code, Ingo Molnar, (Thu Feb 7, 4:37 pm)
Re: [PATCH] Use global TLB flushes in MTRR code, Andi Kleen, (Fri Feb 8, 7:44 am)
Re: [PATCH] Use global TLB flushes in MTRR code, Ingo Molnar, (Sat Feb 9, 5:40 am)
Re: [PATCH] Use global TLB flushes in MTRR code, Andi Kleen, (Sat Feb 9, 7:48 am)
Re: [PATCH] Use global TLB flushes in MTRR code, Ingo Molnar, (Sat Feb 9, 7:47 am)
Re: [PATCH] Use global TLB flushes in MTRR code, Andi Kleen, (Sat Feb 9, 10:12 am)
Re: [PATCH] Use global TLB flushes in MTRR code, Oliver Pinter, (Thu Feb 7, 3:08 pm)