linux-kernel - Re: [PATCH][retry 1] 2.6.27-rc2: invalidate caches before going into suspend

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Date:	Wed, 13 Aug 2008 19:31:15 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mark Langsdorf <mark.langsdorf@....com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH][retry 1] 2.6.27-rc2: invalidate caches before going
	into suspend

(please keep Cc:s intact)

* Mark Langsdorf <mark.langsdorf@....com> wrote:

> @@ -104,6 +103,7 @@ static inline void play_dead(void)
>  	 * With physical CPU hotplug, we should halt the cpu
>  	 */
>  	local_irq_disable();
> +	wbinvd();
>  	while (1)
>  		halt();

hm, why not do what i suggested in my first mail:

        if (cpu >= i486)
                asm("cli; wbinvd; cli; 1: hlt; jmp 1b")
        else
		halt();

perhaps turn it into a wbivd_halt() primitive, to make it clean and even 
more obvious.

This sequence does matter to reliable suspend/resume, and in theory gcc 
could insert something before a halt() as well.

[ i only have a pretty far-fetched example that in all likelyhood wont
  happen in practice: for example halt could be decided to be uninlined
  by a braindead compiler, ftrace could hook in there, and dirty some
  state. But still - the point is that we had a difficult bug in this 
  code for a long time and in such situations we should just over-do 
  robustness by default. ]

	Ingo
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