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

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Message-ID: <20140120082620.GB30183@twins.programming.kicks-ass.net>
Date:	Mon, 20 Jan 2014 09:26:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Len Brown <lenb@...nel.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	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 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).

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