From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC V4 09/10] x86/jump_label: use GENERIC_NOP5_ATOMIC
 instead of jmp5 +0
Date: Fri, 14 Oct 2011 14:52:09 -0700
Message-ID: <4E98AF09.6040306@zytor.com>
References: <cover.1318464169.git.jeremy.fitzhardinge@citrix.com> <34ede5db1571d541a5c3fc49923bb353a37dd431.1318464413.git.jeremy.fitzhardinge@citrix.com> <4E97067A.2070305@zytor.com> <4E9716B8.8050406@goop.org>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Steven Rostedt <rostedt@goodmis.org>, "David S. Miller" <davem@davemloft.net>, David Daney <david.daney@cavium.com>, Michael Ellerman <michael@ellerman.id.au>, Jan Glauber <jang@linux.vnet.ibm.com>, Jason Baron <jbaron@redhat.com>, the arch/x86 maintainers <x86@kernel.org>, Xen Devel <xen-devel@lists.xensource.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
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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@citrix.com>
>>>
>>> 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