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[Xen-devel] Re: [PATCH RFC V4 09/10] x86/jump_label: use GENERIC_NOP5_AT

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH RFC V4 09/10] x86/jump_label: use GENERIC_NOP5_ATOMIC instead of jmp5 +0
From: "H. Peter Anvin" <hpa@xxxxxxxxx>
Date: Fri, 14 Oct 2011 14:52:09 -0700
Cc: the arch/x86 maintainers <x86@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Jan Glauber <jang@xxxxxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Jason Baron <jbaron@xxxxxxxxxx>, David Daney <david.daney@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Michael Ellerman <michael@xxxxxxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>
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On 10/13/2011 09:50 AM, Jeremy Fitzhardinge wrote:
> On 10/13/2011 08:40 AM, H. Peter Anvin wrote:
>> On 10/12/2011 05:08 PM, Jeremy Fitzhardinge wrote:
>>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
>>>
>>> GENERIC_NOP5_ATOMIC should make a better nop.
>>>
>> On 32 bits, yes.  On 64 bits you should use P6_NOP5_ATOMIC.
> 
> So the cleanest way of fixing that is to make the GENERIC_NOP*  be
> defined to P6_NOP* on 64-bit then?  Assuming I'm correct in guessing
> that the intent of GENERIC_NOP* is "a basically good-enough NOP that
> will work on any x86".
> 

No, GENERIC_NOPs are not valid on 64 bits at all.

        -hpa


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