linux-kernel - Re: linux-next: build failure after merge of the tip tree

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Message-ID: <52DCE4CF.2060605@zytor.com>
Date:	Mon, 20 Jan 2014 00:56:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Peter Zijlstra <peterz@...radead.org>, Len Brown <lenb@...nel.org>
CC:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-next@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the tip tree

On 01/20/2014 12:26 AM, Peter Zijlstra wrote:
> On Sun, Jan 19, 2014 at 11:45:43PM -0500, Len Brown wrote:
>> +static void mwait_idle(void)
>> +{
>> +       mwait_idle_with_hints(0, 0);
>> +}
>> +
>>
>> The reason the patch above will crash Core2 machines is because
>> core2 machines don't support mwait_idle_with_hints().
>>
>> The calling sequence for old and new MWAIT instructions is different.
>> The former must be invoked with interrupts enabled,
>> and the later can be invoked with interrupts disabled,
>> which is a feature that Linux takes advantage of.
> 
> What old and new? They're the same byte sequence: 0x0f 0x01 0xc9
> 
> And your 'old' __sti_mwait(0,0) has the exact same arguments as
> mwait_idle_with_hints(0,0).
> 

The difference is the STI!

	-hpa

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